Marine and Fishery sciences 40 (1): xxx-xxx (2027)

https://doi.org/10.47193/mas.4012027010102

Marine and

Fishery Sciences

MAFIS

*Correspondence:

ezzalmatyyouness@gmail.com

Received: 11 August 2026

Accepted: 22 September 2026

ISSN 2683-7595 (print)

ISSN 2683-7951 (online)

https://ojs.inidep.edu.ar

Journal of the Instituto Nacional de

Investigación y Desarrollo Pesquero

(INIDEP)

This work is licensed under a Creative

Commons Attribution-

NonCommercial-ShareAlike 4.0

International License

ORIGINAL RESEARCH

Estimation of seafood byproducts generated by freezing companies in the

Souss-Massa Region, Morocco

ez-zalMaty youness1, 2, *, FatiMa Bellali 2, Maainia saadani 1, 2 and MerieM KharrouBi1

1Laboratory of Biotechnologies, Specialized Center of Valorization and Technology of Sea Products, National Institute of Fisheries

Research (INRH), P.K. 07, Route d’Essaouira, Anza 80000, Agadir, Morocco. 2Biological Engineering Laboratory, Department of

Biology, Faculty of Sciences and Techniques, Sultan Moulay Slimane University, P.O. Box: 523, Beni Mellal, Morocco.

ORCID Ez-zalmaty Youness https://orcid.org/0009-0008-0386-1822, Fatima Bellali https://orcid.org/0000-0002-5236-5330,

Meriem Kharroubi https://orcid.org/0000-0003-4616-7781

ABSTRACT. The seafood processing industry generates substantial quantities of byproducts that

remain underutilized despite their potential for recovery and further utilization. This study aimed

to assess the generation and management of seafood byproducts within the freezing industry of the

Souss-Massa region, Morocco. A voluntary semi-structured survey was conducted among 21 of the

39 regional freezing companies, focusing on raw material supply, processing activities, byproduct

generation, and management practices. Following post-stratication to the regional frame of 39 freez-

ing companies, the estimated annual processed volume was approximately 70,230 t, generating an

estimated 22,504 t of seafood byproducts, corresponding to approximately 32% of the processed raw

material. Byproduct generation varied according to species and product type, with Sardina pilchardus,

Trachurus trachurus, Merluccius merluccius, and Loligo vulgaris contributing the largest estimated

quantities. Viscera (29%), heads (28%), and bones and tails (21%) were dominant byproduct fractions,

while shells and carapaces, skin, and trimmings accounted for smaller proportions. The companies

surveyed reported several management routes, including shmeal production, animal feed, external

management channels, and direct sales. These ndings provide a regional inventory of seafood

byproduct streams that may be considered for future valorization. Their technical, economic, and

environmental feasibility requires further assessment through approaches such as techno-economic

assessment (TEA) and life-cycle assessment (LCA).

Key words: Seafood byproducts, freezing industry, valorization, circular economy, material ow

analysis.

Estimación de los subproductos marinos generados por empresas congeladoras en la región

de Souss-Massa, Marruecos

RESUMEN. La industria de procesamiento de productos del mar genera cantidades considerables

de subproductos que permanecen infrautilizados, a pesar de su potencial de recuperación y aprove-

chamiento posterior. Este estudio tuvo como objetivo evaluar la generación y gestión de subproductos

pesqueros en la industria de congelación de la región de Souss-Massa (Marruecos). Se realizó una

encuesta voluntaria semiestructurada a 21 de las 39 empresas regionales de congelación, centrán-

dose en el suministro de materia prima, actividades de procesamiento, generación de subproductos

y prácticas de gestión. Tras realizar una post-estraticación basada en el universo regional de 39

empresas, se estimó un volumen anual procesado de aproximadamente 70.230 t, generando unas

22.504 t de subproductos pesqueros, lo que equivale a cerca del 32 % de la materia prima procesada.

La generación de subproductos varió según la especie y el tipo de producto. Sardina pilchardus,

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

INTRODUCTION

Aquatic foods play an important role in glob-

al food security, nutrition, and socioeconomic

development, particularly in coastal countries.

They provide high-quality proteins, essential fat-

ty acids, minerals, and vitamins, and represent an

important component of healthy diets (Suresh et

al. 2018; Prelipcean et al. 2022). Global sheries

and aquaculture production reached a record level

in 2022, while apparent per capita consumption

of aquatic animal foods was estimated at 20.7 kg,

highlighting the growing importance of aquatic

food in global food systems (FAO 2024). This in-

crease has been associated with population growth,

changing dietary preferences, and improvements

in processing and distribution systems (Cooney et

al. 2023). Global sheries and aquaculture pro-

duction reached 223.2 million tons in 2022, com-

prising 185.4 million tons of aquatic animals and

37.8 million tons of algae. Approximately 89% of

aquatic animal production was intended for hu-

man consumption, while the remaining share was

used for non-food purposes (FAO 2024). Despite

this production growth, the sector faces increas-

ing pressure on marine resources. In 2021, 62.3%

of the assessed marine sh stocks were exploit-

ed within biologically sustainable levels, whereas

37.7% were overshed. When weighted by pro-

duction, 76.9% of global landings originated from

biologically sustainable stocks (FAO 2024).

Seafood processing also generates heteroge-

neous material streams, including heads, viscera,

bones, skins, trimmings, and shells (Suresh et al.

2018). Their quantity and composition vary ac-

cording to species, body size, product form, and

processing intensity (Venugopal 2021). When these

material streams are poorly quantied or managed,

opportunities for their recovery as sources of pro-

teins, lipids, collagen, minerals, and other valuable

compounds remain limited. Reliable information

on their generation and current management is

therefore necessary to support appropriate recovery

and valorization strategies(Caruso 2015).

In Morocco, the sheries sector is a major com-

ponent of the national blue economy. Supported

by a coastlines extending approximately 3,500 km,

the country is among the principal producers and

exporters of seafood products in Africa (Nejjari

and Elyous 2023; Boudad et al. 2025). National

sheries production reached approximately 1.42

million tons in 2023, with a reported value of USD

1.59 billion (DPM 2023a). In the same year, the

seafood-processing sector comprised 518 establish-

ments covering freezing, fresh-product packaging,

canning, semi-preserving, and shmeal and sh-oil

production, with freezing companies representing

the dominant category (DPM 2023b).

The Souss-Massa region occupies a major po-

sition in this processing network, accounting for

more than 19% of national freezing companies and

nearly 40% of all seafood-processing establish-

ments (DPM 2023b). Although these companies

contribute to employment and regional economic

activity, their processing operations generate sub-

stantial streams of seafood byproducts alongside

Trachurus trachurus, Merluccius merluccius y Loligo vulgaris fueron las especies que aportaron las mayores cantidades estimadas. Las

vísceras (29 %), cabezas (28 %) y espinas y colas (21 %) constituyeron las fracciones predominantes de subproductos, mientras que las

conchas y caparazones, piel y recortes representaron proporciones menores. Las empresas encuestadas informaron sobre diversas vías de

gestión, incluidas la producción de harina de pescado, alimentación animal, canales de gestión externa y venta directa. Estos resultados

proporcionan un inventario regional de los ujos de subproductos pesqueros que podrían considerarse para su futura valorización. Su

viabilidad técnica, económica y ambiental requiere una evaluación más exhaustiva mediante enfoques como la evaluación técnico-eco-

nómica (TEA) y el análisis de ciclo de vida (ACV).

Palabras clave: Subproductos de origen marino, industria de la congelación, valorización, economía circular, análisis de ujo de materiales.

Youness et al. estimation of seafood bY-products in the souss-massa region 3

other waste streams. In this study, seafood byprod-

ucts refer to biological fractions generated during

processing and are potentially available for further

use, whereas other waste streams are considered

separately. However, quantitative information on

the species-specic generation, composition, man-

agement, and recovery of these materials remain

limited in Morocco. National and sectoral statistics

describe sheries production, processing activities,

and the structure of the Moroccan seafood-pro-

cessing industry (DPM 2023b), but provide limited

information linking individual freezing companies,

processed species, byproduct generation, and re-

ported management pathways . Previous national

assessments have mainly provided aggregated or

subsector-level estimates, whereas international

studies have documented seafood byproduct gener-

ation and valorization across a range of processing

contexts (Erasmus et al. 2021; Venugopal 2021;

Cooney et al. 2023). This information gap limits

the assessment of potentially available byproduct

streams and the development of evidence-based

recovery and further-use strategies.

Therefore, this study aimed to estimate the quan-

tities and characterize the composition of seafood

byproducts generated by freezing companies in

the Souss-Massa region, examine their distribution

according to species and processed product, and

assess the existing management and recovery prac-

tices. The study also sought to identify reported

constraints to byproduct valorization and explore

respondents’ awareness of potential valorization

pathways.

MATERIALS AND METHODS

Study area

The Souss-Massa region is one of Morocco’s

major seafood processing hubs, with a high con-

centration of freezing companies located in the

Agadir industrial area. According to the Maritime

Fisheries Delegation (DPM 2023b), the regional

sampling frame comprised 39 freezing companies

processing a wide range of marine resources. These

companies generate substantial quantities of sea-

food byproducts; however, no comprehensive re-

gional database describing byproduct generation,

management, and valorization is currently avail-

able. To address this gap, 21 of the 39 freezing

companies participated in the study. Participating

companies were in the main industrial zones of

Agadir: (a) Anza, (b) New and Old Port (N.Port),

Survey design and data collection

Face-to-face interviews were conducted with

company representatives, including directors, pro-

duction managers, quality managers, and health,

safety and environment (HSE) ofcers. The ques-

tionnaire was pre-tested in three companies select-

ed from three different industrial zones, to assess

its clarity and identify any necessary adjustments.

These companies were subsequently re-interviewed

using the nalized questionnaire to complete the

additional or revised questions. All 39 freezing

companies identied in the regional sampling

frame were contacted. Twenty-one agreed to partic-

ipate in the survey and were interviewed, whereas;

the remaining 18 companies did not participate.

Data were collected between May and July

2025 in either French or Moroccan Arabic (Dari-

ja), depending on the respondent’s preference.

Interviews lasted approximately 30-50 min. This

approach allowed standardized data collection with

the exibility to obtain detailed technical and op-

erational information, particularly where ofcial

datasets were unavailable. To ensure condential-

ity, all participating companies were anonymized,

and the results were presented in aggregated form.

The questionnaire consisted of 47 questions organ-

ized into six thematic sections covering company

characteristics, raw material supply, processing

activities, byproduct generation, current manage-

ment practices, and environmental management.

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

The questionnaire was pre-tested in three freezing

companies to improve its structure and clarity be-

fore the main data collection. Annual processed

volumes referred to the 2024-2025 reference period

and were recorded in tons.

Before each interview, the objectives of the

study were explained to the participants, and oral

informed consent was obtained. The questionnaire

covered company characteristics, sources of raw

materials, annual processing volumes, processed

species, byproduct generation, management prac-

tices, and valorization pathways. Missing or un-

available responses were not imputed and were

excluded from the corresponding descriptive anal-

Figure 1. Map of study area; Anza industrial zone (A), New Port and Old Port (N.Port) (B), Tassila industrial zone (C), Haliopole

industrial park (D).

Youness et al. estimation of seafood bY-products in the souss-massa region 5

yses. To complement survey information, second-

ary information was obtained from the Maritime

Fisheries Delegation (DPM), the National Ofce of

Fisheries (ONP), and Customs authorities. These

institutional sources were used to contextualize the

information collected during the interviews.

Estimation of seafood byproduct generation

Conversion factors

Quantities of seafood byproducts generated by

the surveyed freezing companies were estimated

by combining annual processing volumes reported

during the interviews with species-specic conver-

sion factors obtained either through in-plant meas-

urements, where feasible, or from FAO sources

when direct measurements were unavailable. These

conversion factors represented cumulative mass

changes across successive processing stages were

species-specic. For each species for which con-

version factors were directly determined, three in-

dependent processing lots were monitored (Table

1). Each lot was weighed before processing and

after each successive processing stage. The cumu-

lative conversion factor for species s at stage j was

calculated as the ratio of the mean initial mass of

the three lots to the mean remaining mass after

stage j:

where Ms.0 is the mean initial mass of the replicate

lots of species s before processing and Ms.j is the

mean mass remaining across the same lots after

processing stage j. Because the same number of

replicates lots was used for both means, the ratio

of means is mathematically equivalent to the ratio

of the total initial mass to the total remaining mass

of the monitored lots. This pooled mass-based

conversion factor was used because it was subse-

quently applied to industrial mass ows. Standard

errors were calculated from the paired initial and

remaining mass measurements using rst-order er-

ror propagation, including the covariance between

paired measurements:

where (S2M0 and S2Mj are the sample variances

of the initial and remaining masses, respectively,

SM0,Mj is their covariance, and (n = 3). Because cu-

mulative conversion factors at successive process-

ing stages were derived from the same replicate

lots, their uncertainties were correlated and were

not considered independent.

Byproduct estimation

Because processing forms varied according to

customer requirements, a species-specic set of

applicable processing pathways was used for the

estimation. The quantity of byproducts generated

at each processing stage was estimated as the dif-

ference between the remaining masses immediately

before and after that stage, using the corresponding

cumulative conversion factors according to the fol-

lowing relationship:

where Mi.s.0 denotes the initial processed mass of

species s in company i and CFs.J-1 and CFs.J repre-

sent the cumulative conversion factors correspond-

ing to the processing stages immediately before

and after stage j, respectively. For the initial un-

processed state, CFs,0 = 1

Regional estimation and mass-balance assessment

Post-stratication. Regional quantitative estimates

were obtained using post-stratication by industrial

zones rather than direct unweighted extrapolation

from the 21 participating companies. Because the

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

Table 1. Species-specic cumulative conversion factors (CF) according to successive processing stages. Values for directly measured conversion factors are

presented as CF ± SE. WR: whole round (CF = 1); G: gutted; GH: gutted and headed; GHS: gutted, headed and skinned; B&T: bones and tail; IS.:

internal structure; Sh: shelling; TR: trimming. NA: not applicable; ND: not determined. Magallana gigas is reported as Crassostrea gigas in the cor-

responding source. *: FAO (2000).

Species CF-G CF-GH CF-GHS CF B&T CF-IS CF-Sh CF-TR

Merluccius merluccius 1.213 ± 0.010 1.502 ± 0.034 1.624 ± 0.021 2.160 ± 0.067 NA NA 2.204 ± 0.037

Sparus aurata 1.103 ± 0.011 1.141 ± 0.010 1.181 ± 0.001 1.420 ± 0.017 NA NA 1.436 ± 0.023

Argyrosomus regius 1.055 ± 0.013 1.142 ± 0.015 1.190 ± 0.001 1.400 ± 0.006 NA NA 1.404 ± 0.017

Macruronus magellanicus 1.072 ± 0.012 1.270 ± 0.013 1.394 ± 0.016 1.680 ± 0.007 NA NA 1.736 ± 0.021

Pomatomus saltatrix 1.115 ± 0.009 1.184 ± 0.015 1.243 ± 0.009 1.570 ± 0.022 NA NA 1.606 ± 0.016

Mycteroperca rubra 1.128 ± 0.040 1.369 ± 0.031 1.428 ± 0.034 1.840 ± 0.010 NA NA 2.005 ± 0.023

Seriola dumerili 1.043 ± 0.015 1.149 ± 0.003 1.186 ± 0.009 1.460 ± 0.016 NA NA 1.479 ± 0.015

Trachurus trachurus 1.115 ± 0.014 1.474 ± 0.037 1.643 ± 0.053 1.800 ± 0.049 NA NA 1.825 ± 0.009

Sardina pilchardus 1.055 ± 0.012 1.184 ± 0.004 1.213 ± 0.013 1.490 ± 0.019 NA NA 1.521 ± 0.015

Engraulis encrasicolus 1.032 ± 0.006 1.546 ± 0.003 1.703 ± 0.018 1.860 ± 0.013 NA NA 1.864 ± 0.013

Sarda sarda 1.103 ± 0.026 1.307 ± 0.009 1.418 ± 0.043 1.990 ± 0.009 NA NA 2.256 ± 0.024

Lepidopus caudatus 1.090 ± 0.010 1.229 ± 0.011 1.327 ± 0.019 1.510 ± 0.015 NA NA 1.533 ± 0.017

Octopus vulgaris 1.088 ± 0.089 1.128 ± 0.079 NA NA NA NA 1.135 ± 0.077

Loligo vulgaris 1.155 ± 0.014 1.183 ± 0.015 NA NA 1.227 ± 0.018 NA 1.234 ± 0.011

Sepia ofcinalis 1.128 ± 0.011 1.161 ± 0.011 NA NA 1.163 ± 0.032 NA 1.188 ± 0.036

Magallana gigas* ND ND ND ND ND 5.33 ND

Mytilus galloprovincialis* ND ND ND ND ND 5 ND

Parapenaeus longirostris* ND ND ND ND ND 1.05 ND

Youness et al. estimation of seafood bY-products in the souss-massa region 7

information available for non-participating com-

panies was limited to their industrial-zone location,

respondent-nonrespondent comparisons were re-

stricted to zone distribution (Little 1993; Valliant

1993). For each zone k, a post-stratication weight

wk was assigned, where Nk denotes the number of

companies in the regional sampling frame and nk

the number of surveyed freezing companies (Table

2):

The reported processing tonnage of each surveyed

companies and the estimated species-specic

byproduct quantities within each company were

extrapolated to the regional level using the corre-

sponding zone-specic post-stratication weight.

The regional total was estimated as:

where yki represents either the reported processing

tonnage or the estimated byproduct quantity for

participating facility i in zone k.

Sensitivity analysis

Because annual processing volumes were report-

ed as point estimates without associated uncertainty

bounds, formal condence intervals could not be

derived. Uncertainty related to extrapolation to the

18 non-participating freezing companies was there-

fore assessed using a deterministic sensitivity anal-

ysis based on the variability observed among par-

ticipating companies within each industrial zone.

For each zone k, three scenarios were dened for

non-participating companies: a lower scenario us-

ing the minimum observed processing volume, a

base scenario using the mean, and an upper sce-

nario using the maximum. Reported volumes of

participating companies remained unchanged. The

estimated processed volume for zone k under sce-

nario z was calculated as:

where Yki is the reported processing volume of

participating facility i, and Yk(z) represents the ob-

served minimum, mean, or maximum processing

volume among participating companies in zone k.

Regional estimates were obtained by summing the

zone-specic estimates.

The base scenario was mathematically equiva-

lent to the post-stratied estimate. Species com-

position and conversion factors for the processed

raw material were kept constant, while only the

assumed processing volume of non-participating

companies changed. Additional deterministic sen-

sitivity analyses were conducted separately for spe-

Table 2. Regional sampling frame, participation, and post-stratication weights by industrial zone.

Industrial zone Regional frame (Nk) Participating (nk) Non-participating Weight (Nk/nk)

N.Port 20 9 11 2.222

Anza 7 3 4 2.333

Tassila 5 5 0 1.000

Haliopole 7 4 3 1.750

Total 39 21 18 -

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

cies composition and conversion factors. Species

composition sensitivity was assessed using the

lowest- and highest-byproduct-yielding company

proles observed within each zone, while keep-

ing total processed volume and conversion factors

unchanged (See Supplemental Material). A local

deterministic sensitivity check for conversion fac-

tors was performed by varying directly measured

cumulative conversion factors as CF-SE, CF, and

CF + SE, while factors without reported standard

errors were kept constant. This was not considered

a full propagation of joint uncertainty. Resulting

ranges were interpreted as deterministic sensitivity

scenarios rather than statistical condence intervals

(Table 3).

Internal computational consistency check

Internal computational consistency was assessed

for each modeled processing pathway by conrm-

ing that the initial processed mass was equal to

the nal remaining product mass plus the sum of

the byproduct fractions removed during successive

processing stages:

The check was restricted to the modeled solid

biological fractions and did not include wastewa-

ter, melted ice, packaging, or other non-modeled

processing streams

Data processing and analysis

Survey responses were compiled, organized, and

processed using R version 4.5.0. Data processing

and graphical analyses were performed using the

dplyr (version 1.1.4), tidyr (version 1.3.1), and

ggplot2 (version 4.0.3) packages. Descriptive

analyses included frequencies, percentages, totals,

and graphical summaries. Categorical results were

reported as n/N (%), with N corresponding to the

number of valid responses for each item, while

multiple-response items were analyzed separately.

Post-stratication weights were applied only to re-

gional quantitative estimates, whereas descriptive

survey results were reported for participating com-

panies without weighting. No inferential statistical

tests were applied to estimated byproduct tonnages.

Study limitations

The quantities reported in this study should be

regarded as estimates derived from company-re-

Table 3. Deterministic Sensitivity Analysis of Regional Processed raw material and Seafood byproduct estimates.

Sensitivity factor Scenario Processed Estimated Byproducts/processed

volume (t) byproduct (t) volume (%)

Processed raw material volume Lower 53,050 16,794 31.66

Base 70,230 22,504 32.04

Upper 84,659 27,294 32.24

Species composition Lower 70,230 20,080 28.59

Base 70,230 22,504 32.04

Upper 70,230 25,412 36.18

Conversion factors Lower 70,230 21,302 30.33

Base 70,230 22,504 32.04

Upper 70,230 23,603 33.61

Youness et al. estimation of seafood bY-products in the souss-massa region 9

ported processing volumes and species-specic

conversion factors rather than from direct annu-

al measurements. Destination-specic byproduct

tonnages could not be quantied or independently

veried because systematic company-level records

were generally unavailable.

RESULTS

Characteristics of surveyed seafood processing

companies

Companies surveyed were characterized based

on their years of operation and workforce struc-

ture (Table 4). Considerable heterogeneity was

observed in both company age and workforce size

among the 18 companies with valid responses. Ap-

proximately 83% had been operating for more than

15 years, with a mean operating age of approxi-

mately 21 years. Workforce size differed marked-

ly among companies, particularly in terms of em-

ployment status. The number of seasonal workers

ranged from 6 to 110, whereas that of permanent

employees ranged from 15 to 141 companies.

Sources of raw material supply

To better understand the dynamics of byproduct

generation in seafood freezing companies operat-

ing in the Souss-Massa region, it was necessary to

examine their raw material supply patterns.

Most companies obtained their raw materials

from seafood traders, while 26% operated their own

shing eets. However, according to the compa-

nies surveyed, locally available volumes were in-

sufcient to meet their requirements, particularly

during shing closure periods. Consequently, some

companies relied on imports to supplement local

supplies, meet their raw material needs, and main-

tain production continuity. Raw materials were re-

ceived in several forms. Fresh sh stored under ice

in polystyrene containers was reported by 95% of

the companies surveyed. Fresh products were also

received in refrigerated boxes or transported in bulk

using insulated trucks, with each mode reported by

63% of the companies. In addition, frozen sh in

blocks was reported by 68.4% of companies, while

cartons and bags were reported by 73.7% and 68.4%,

respectively (Figure 2; Table 5). Nevertheless, no

formal system was identied for recording or mon-

itoring the quantities of packaging waste generated.

Table 4. Company age and workforce characteristics among surveyed freezing companies with valid responses (N = 18). Note:

Workforce values represent the total numbers of seasonal and permanent = workers reported by all companies within each

company-age group.

Company age group (years) Seasonal workers (total) Permanent workers (total) Companies n/N (%)

0-5 49 97 2/18 (11.1)

6-10 0 0 0/18 (0.0)

11-15 16 34 1/18 (5.6)

16-20 85 33 5/18 (27.8)

21-25 110 141 5/18 (27.8)

26-30 42 112 1/18 (5.6)

31-35 26 57 3/18 (16.7)

36-45 6 15 1/18 (5.6)

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

Information on the disposal destinations of packag-

ing waste was also not systematically documented.

Respondents identied shing closure periods,

limited coordination among supply-chain actors,

and rising energy prices as constraints affecting

raw material availability. They also perceived these

factors as contributing to higher raw material prices

and increased competition among seafood-process-

ing companies.

Composition and quantication of byproducts

The estimated byproduct quantities were ob-

tained by combining the processed volumes re-

ported by the surveyed freezing companies with

species- and product-specic conversion factors.

These factors varied according to both species and

processing stage, with whole-round products as-

signed a reference conversion factor of 1 (Table 1).

The post-stratied regional estimate indicated that

approximately 70,230 t of seafood was processed

during the reference period, generating an estimat-

ed 22,504 t of seafood byproducts, corresponding

to approximately 32% of the estimated processed

mass. Regional estimates showed that viscera and

heads represented the two largest byproduct frac-

tions, accounting for approximately 6,530 t (29%)

and 6,347 t (28%) of the total estimated byproduct

Figure 2. Sources of raw material supply reported by the responding companies (N = 19).

100

Importation Partner companies Fish traders Company owneed-ﬂit

Percentage %()

Sources

Table 5. Product state Reception mode Proportion n/N (%).

Product state Reception mode Proportion n/N (%)

Fresh sh Ice-lled containers (18/19) 95

Refrigerated cartons (12/19) 63

Bulk (12/19) 63

Frozen sh Frozen blocks (13/19) 68

Cartons (14/19) 74

Bags (13/19) 68

Youness et al. estimation of seafood bY-products in the souss-massa region 11

quantity, respectively. Bones and tails ranked third,

representing approximately 4,669 t (21%). Togeth-

er, these three fractions accounted for nearly 80%

of the estimated byproducts. Shells and carapaces,

skin, and trimmings accounted for smaller propor-

tions (Table 6).

Species-specic estimates revealed differences in

each species contribution to total regional byprod-

uct generation. Sardina pilchardus represented the

largest contribution (16.3%), followed by Trachurus

trachurus (12.2%) and Merluccius merluccius

(10.8%). Cephalopods also contributed substantially,

particularly Loligo vulgaris (8.0%), Sepia ofcina-

lis (7.5%) and Octopus vulgaris (5.1%) (Table 7;

Figure 3). Among demersal sh, Merluccius mer-

luccius generated the highest quantity of byprod-

ucts, whereas Sardina pilchardus and Trachurus

trachurus predominated among pelagic species.

Among cephalopods, Loligo vulgaris and Sepia of-

cinalis generated the largest quantities, while bi-

valve byproducts consisted almost entirely of shells.

Despite differences among species, viscera, heads,

bones and tails remained the predominant byproduct

fractions in most sh species (Table 7; Figure 3).

Sensitivity analysis of regional estimates

The deterministic sensitivity analysis showed

that the estimated regional processed volume varied

from 53,050 t under the lower scenario to 84,659

t under the upper scenario, with a base estimate of

70,230 t. The corresponding byproduct estimates

were 16,794 t, 22,504 t, and 27,294 t, respectively.

When processed volume was held constant, varia-

tion in species composition resulted in byproduct

estimates ranging from 20,080 to 25,412 t, where-

as the local deterministic perturbation of directly

measured conversion factors using CF-SE and CF

+ SE resulted in estimated byproduct quantities

ranging from 21,302 to 23,603 t. These values

represent deterministic sensitivity scenarios and

should not be interpreted as statistical condence

intervals (Table 3).

Byproduct management practices

The survey included specic questions regarding

the implementation of Environmental Management

Systems (EMS). Among the 19 companies provid-

ing valid responses, 12/19 (63.2%) reported hav-

ing no plans to implement an EMS, 6/19 (31.6%)

were in the process of implementing one, and only

1/19 (5.3%) reported having an operational EMS

(Figure 4).

In addition to solid seafood byproducts, the sur-

veyed freezing companies also generated liquid

efuents during processing operations. Liquid ef-

uents were considered separately and were not

Table 6. Regional estimated quantities of seafood byproducts by category.

Byproduct fraction Quantity (t) Percentage (%)

Viscera 6,530 29.0

Heads 6,347 28.0

Skin 1,767 8.0

Bones and tails 4,669 21.0

Trimmings 886 4.0

Shells and carapaces 1,999 9.0

Internal structures 305 1.0

Total 22,504 100.0

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

Figure 3. Heatmap of post-stratied regional seafood byproduct estimates (t) by species and fraction. F = sh; C = cephalopods;

B = bivalves Cr = crustaceans.

Table 7. Post-stratied regional model estimates of seafood byproducts by species for the 2024-2025 reference period. Values are

presented as estimated tonnes and percentage of total estimated by-product mass.

Species Estimated byproducts (t) Byproduct share (%)

Merluccius merluccius 2,430.5 10.8

Sparus aurata 396.1 1.8

Argyrosomus regius 118.9 0.5

Macruronus magellanicus 1,270.1 5.6

Pomatomus saltatrix 15.0 0.1

Mycteroperca rubra 1,004.1 4.5

Seriola dumerili 88.8 0.4

Trachurus trachurus 2,735.4 12.2

Sardina pilchardus 3,660.9 16.3

Engraulis encrasicolus 1,064.9 4.7

Sarda sarda 1,418.1 6.3

Lepidopus caudatus 1,642.4 7.3

Octopus vulgaris 1,149.4 5.1

Loligo vulgaris 1,810.6 8.0

Sepia ofcinalis 1,698.6 7.5

Magallana gigas 1,047.8 4.7

Mytilus galloprovincialis 950.5 4.2

Parapenaeus longirostris 0.9 0.0

Youness et al. estimation of seafood bY-products in the souss-massa region 13

included in the quantitative byproduct estimates.

Among the 19 companies providing valid respons-

es, 2/19 (10.5%) reported having a wastewater

treatment plant (WWTP), whereas 17/19 (89.5%)

reported having no dedicated wastewater treatment

system. No formal monitoring system for waste-

water discharges was reported in the survey. The

survey documented wastewater management prac-

tices as reported by participating companies, while

discharge events and environmental performance

were not independently assessed.

The surveyed companies reported using several

external routes for the management or utilization of

seafood byproducts. Transfer to external shmeal

producers and animal feed were each reported by

15/19 (78.9%) of the responding companies, while

19/19 (100%) reported disposal to a public landll,

and 4/19 (21.1%) reported direct sales. One facility,

1/19 (5.3%), reported another destination (Figure

5). Companies could report more than one desti-

nation; therefore, percentages do not rise to 100%.

These categories were not mutually exclusive, as

companies could use different routes for different

byproduct streams. These percentages represent the

proportion of companies reporting each destination

rather than the share of byproduct tonnage allocat-

ed to each route or the frequency of use of each

destination. No on-site valorization was reported,

and destination-specic quantities could not be es-

timated because systematic records of byproduct

ows by destination were unavailable.

Regarding perceived barriers, surveyed compa-

nies reported several constraints affecting further

seafood byproduct utilization (Figure 6). Finan-

cial constraints were reported by 9/19 companies

(47.4%), followed by regulatory constraints report-

ed by 8/19 (42.1%), limited technical expertise

by 5/19 (26.3%), lack of market outlets by 4/19

(21.1%), and limited availability of qualied per-

sonnel by 1/19 (5.3%). Multiple responses were al-

lowed; therefore, percentages do not sum to 100%.

DISCUSSION

This study provides a regional assessment of

seafood byproduct generation and management

practices in the freezing industry of the Souss-Mas-

sa region, Morocco. The regional quantities should

be interpreted as conditional modeled estimates de-

rived from voluntary participation and zone-based

post-stratication. Based on annual processing

volumes and species-specic conversion factors,

the post-stratied regional estimates indicated ap-

proximately 22,504 t of seafood byproducts from

Figure 4. Environmental management system (EMS) status reported by the responding companies (N = 19).

100

EMS in progress Without EMSEMS

Percentage %()

EMS status

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

an estimated processed biomass of 70,230 t, cor-

responding to approximately 32% of the estimated

processed raw material. These estimates refer only

to the modeled solid biological fractions included

in the study and should not be interpreted as total

facility waste or as veried recoverable materi-

al. The deterministic sensitivity analyses further

showed that the regional estimate was inuenced

by assumptions regarding processed raw material

volume, species composition, and conversion fac-

tors. These deterministic scenarios should not be

interpreted as condence intervals. These ndings

provide a quantitative estimate of seafood byprod-

uct generation in the Souss-Massa freezing com-

panies and may contribute to broader resource-ef-

ciency objectives consistent with Sustainable

Development Goal 12 (Responsible Consumption

and Production).

The estimated proportion of byproducts (32%)

was inuenced by the species and processing

pathways represented in the companies surveyed.

Differences in byproduct generation among sea-

Figure 6. Reported constraints to further seafood byproduct utilization among surveyed freezing companies (N = 19).

Financial constraints

Regulatory constraints

Limited technical expertise

Lack of market outlets

Limited availability of qualiﬁed personnel

Figure 5. Seafood byproduct destinations reported by the responding companies (N = 19). Multiple responses were allowed; per-

centages are unweighted, may overlap, and represent neither tonnage allocation nor frequency of use.

100

Fishmealproduction Animal feed External disposalDirectsales

Percentage %()

Byproductestinationd

Youness et al. estimation of seafood bY-products in the souss-massa region 15

food-processing operations are generally associat-

ed with the processed species, processing technol-

ogy, and nal commercial products (Coppola et al.

2021; FAO 2022; Cassol et al. 2025). This variabil-

ity supports the use of species- and product-specic

conversion factors rather than a single generalized

factor. Variability in raw material supply may also

contribute to temporal changes in species availa-

bility and processed volumes.

The composition of byproducts was strongly

inuenced by the processed species. The predom-

inance of sh-derived byproducts and of viscera,

heads, and bones and tails reects the routine

evisceration and heading operations applied be-

fore freezing. Comparable distributions have been

reported in other seafood-processing industries,

where viscera, heads, skeletons, skins, and shells

represent major byproduct streams (Nawaz et al.

2020; Erasmus et al. 2021). This information may

support the preliminary screening of potential uti-

lization pathways; however, their technical and

economic feasibility may also depend on factors

such as material quality and preservation, process-

ing yields, logistics, market conditions, regulatory

requirements, and costs.

Beyond their quantitative importance, seafood

byproducts may provide feedstocks for further

utilization of pathways. Numerous studies have

reported that sh skins, bones, viscera, scales, and

shells are rich in collagen, gelatin, bioactive pep-

tides, omega-3 polyunsaturated fatty acids, miner-

als, chitin, and chitosan, with potential applications

in the food, pharmaceutical, cosmetic, biomedi-

cal, and agricultural sectors (Felician et al. 2018;

Nikoo et al. 2023; Elhiss et al. 2024; Mkadem

and Kaanane 2024). These reported applications

indicate potential pathways for further utilization;

however, their technical and economic feasibility

in the Souss-Massa context was not evaluated in

the present study.

Among the identied by-product fractions, the

skin of Mycteroperca rubra is discussed only as

a hypothesis for future screening because it was

mechanically separated as a distinct by-product

stream during processing. Fish skin is recognized

as a potential marine source of collagen and gelatin,

compounds investigated for applications in tissue

engineering, wound healing, cosmetics, and nu-

traceuticals because of their biocompatibility and

potentially lower risk of disease transmission com-

pared with mammalian collagen (Ge et al. 2020;

Zou et al. 2024). However, no biochemical, safety,

recoverable-yield, market, or feasibility data were

collected for M. rubra in the present study; there-

fore, its potential for further utilization remains

to be evaluated. Despite the potential for further

utilization, the surveyed companies reported sev-

eral conventional routes for the management or

utilization of seafood byproducts, including sh

meal production, animal feed, disposal to a public

landll, and direct sales. However, destination-spe-

cic tonnages were unavailable; therefore, the pro-

portion of total byproduct mass allocated to each

route could not be quantied. The frequency with

which each route was used was also not quanti-

ed. None of the surveyed companies reported

industrial-scale extraction of collagen, gelatin, bi-

oactive peptides, marine oils, or other high-value

compounds. These ndings indicate that such high-

er-value biorenery applications were not reported

among the surveyed companies, rather than estab-

lishing the overall stage of circular-bioeconomy

development in the Moroccan seafood-processing

sector. Nevertheless, several Moroccan studies

have investigated related valorization approaches.

Kharroubi et al. (2021) developed wound-dressing

materials based on shrimp-shell-derived chitosan,

while Aboudamia et al. (2020) extracted chitin

and characterized chitosan obtained from Sardina

pilchardus scales. In a subsequent study, Abouda-

mia et al. (2022) showed that Sardina pilchardus

scales contain both organic and inorganic phases

and exhibit a porous, brous structure, supporting

their potential as a source of marine biomaterials.

These studies illustrate research activity in this eld

in Morocco, but the present survey identied no

corresponding industrial-scale extraction among

the responding companies. Strengthening collabo-

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

ration between research institutions, seafood-pro-

cessing companies, and public stakeholders could

support future technology transfer and pilot-scale

evaluation of these pathways.

Emerging green technologies, including ultra-

sound-assisted, microwave-assisted, and supercriti-

cal uid extraction, have been investigated as alter-

native approaches for recovering compounds from

biological byproducts (Silotry et al. 2021; Hassoun

et al. 2023) However, their applicability to seafood

byproduct streams in the Souss-Massa region was

not evaluated in the present study. Their technical,

economic, and environmental performance would

require dedicated characterization, techno-econom-

ic assessment (TEA), and life-cycle assessment

(LCA), including assessments of extraction yields,

energy and solvent use, processing scale, capital

and operating costs, and product quality.

Despite these potential pathways, the respond-

ents reported several nancial, regulatory, technical,

and market-related constraints to further byproduct

utilization. Only a small proportion of the surveyed

companies implemented an operational environ-

mental management system, reecting limited re-

ported adoption of formal EMS among respondents

rather than providing a direct measure of overall

environmental performance. In addition, seafood

byproducts are highly perishable and require rapid

collection, preservation, and processing to prevent

microbial degradation and quality loss ( Yusoff et

al. 2024). In addition, the literature has identied

contaminants such as heavy metals as a potential

concern in certain seafood byproducts. Although

no chemical measurements were performed in the

present study, this highlights the importance of fu-

ture quality and safety assessments before their use

in food or biomedical applications (Honrado et al.

2024; Younis et al. 2024).

Overall, this study indicates that the seafood

freezing industry in the Souss-Massa region gener-

ates substantial quantities of biological byproducts

that may provide feedstocks for further utilization.

Further evaluation of these streams will require

consideration of regulatory requirements, stronger

collaboration between academia and industry, and

technical and economic assessments of candidate

utilization pathways. Future studies should com-

plement the present estimates with direct industri-

al measurements, further validation of conversion

factors, biochemical characterization, techno-eco-

nomic analyses, and life-cycle assessments to eval-

uate the feasibility and environmental performance

of potential seafood byproduct management and

utilization strategies within a circular bioeconomy

framework.

Although this study provides a regional as-

sessment of seafood byproduct generation and

management in Souss-Massa freezing companies,

several limitations should be acknowledged. Esti-

mates were based on company-reported processed

volumes and species-specic conversion factors

because systematic records of byproduct genera-

tion and destination were generally unavailable;

therefore, the quantities assigned to each man-

agement or utilization pathway could not be de-

termined. Moreover, only 21 of the 39 freezing

companies in the regional sampling frame partic-

ipated in the survey, and information available for

non-participating companies was limited to their

industrial-zone location. Consequently, residual

nonresponse bias cannot be excluded despite the

use of zone-based post-stratication and sensi-

tivity analysis. The resulting regional quantities

should therefore be interpreted as zone-calibrated

estimates conditional on the observed respondent

proles and the assumptions applied to non-par-

ticipating companies. Differences from previous

studies may reect variations in species composi-

tion, processing pathways, product forms, industri-

al scale, and estimation methods. Consistent with

FAO guidance, conversion factors may also vary

for the same species depending on the processing

method applied (FAO 2000). Processing route un-

certainty could not be quantied because no stand-

ard species-specic route or information on the

frequency of alternative routes was available from

the survey. The sensitivity ranges reported in this

study represent deterministic scenarios rather than

Youness et al. estimation of seafood bY-products in the souss-massa region 17

condence intervals. Nevertheless, the approach

may provide a structured framework for estimat-

ing regional material ows where direct annual

byproduct measurements are unavailable and pro-

vides a basis for future monitoring and validation

studies.

CONCLUSIONS

This study provides a regional assessment of sea-

food byproduct generation and management prac-

tices in the freezing industry of the Souss-Massa

region, based on data collected from 21 participat-

ing freezing companies and zone-based post-strat-

ication to the regional frame of 39 companies.

By combining reported annual processing volumes

with species-specic conversion factors, the study

provides an estimate of regional seafood byproduct

ows and documents the management practices

reported by participating companies.

The post-stratied regional processed volume

was estimated at approximately 70,230 t, associat-

ed with approximately 22,504 t of seafood byprod-

ucts, corresponding to approximately 32% of the

estimated processed raw material. The processed

raw material sensitivity analysis produced byprod-

uct estimates ranging from approximately 16,794 t

under the lower scenario to 27,294 t under the up-

per scenario, indicating that the regional estimate

was sensitive to the assumed processing volumes of

non-participating companies. Additional sensitiv-

ity analyses also showed that species composition

and conversion factors inuenced the regional es-

timate. These ranges represent deterministic sce-

narios rather than condence intervals. The results

also showed that byproduct composition varied

according to the processed species and processing

pathways, with viscera and heads among the major

estimated fractions.

The companies surveyed reported several man-

agement and utilization routes, including shmeal

production, animal feed, disposal to a public land-

ll, and direct sales. These responses indicate the

routes used by companies but do not represent

destination-specic tonnage shares or frequency

of use, because systematic records of these ows

were unavailable.

The estimates remain subject to uncertainty

related to company-reported processing volumes,

extrapolation to non-participating companies, pro-

cessing pathways, and the conversion factors used.

They should therefore be interpreted as conditional

on the observed respondent proles and the as-

sumptions used for non-participating companies.

Future studies should prioritize direct industrial

measurement of annual byproduct ows, further

validation of conversion factors, and improved

recording of destination-specic quantities. Bio-

chemical characterization, techno-economic assess-

ment, and life-cycle assessment could subsequently

be used to evaluate specic utilization pathways

and their technical, economic, and environmental

performance.

ACKNOWLEDGEMENTS

Financial support for this research was provided

by the National Center for Scientic and Technical

Research (CNRST), Morocco, through a research

grant awarded under the excellence scholarship

program. The authors also acknowledge this nan-

cial support. Authors acknowledges also the Asso-

ciation ACOPMER, Morocco, for facilitating con-

tact with some of its member freezing companies.

Declaration of interest

The authors declare there are no conicts of in-

terest related to this study.

Use of articial intelligence tools

During the preparation of this manuscript, arti-

cial intelligence tools (ChatGPT, OpenAI, and Per-

Marine and Fishery sciences 40 (1): xxx-xxx (2027)

plexity) were used to assist with English-language

editing, reformulation, and improving clarity and

coherence. The data, calculations, research objec-

tives, methodological choices, scientic interpre-

tations, and conclusions were provided, reviewed,

and validated by the authors, who retain full re-

sponsibility for the scientic content of the study.

Author contribution

Ez-Zalmtay Youness: writing original draft; con-

ducts surveys; data curation; visualization and con-

ceptualization. Fatima Bellali: supervision; writing,

review and editing; methodology; data curation

and conceptualization. Maainia Saadani: writing

original draft. Meriem Kharroubi: writing, review

and editing, supervision; methodology; project

administration.

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