MARINE AND FISHERY SCIENCES 34 (2): 269-274 (2021)
https://doi.org/10.47193/mafis.3422021010604
ABSTRACT. Seahorses (Genus Hippocampus) are rarely reported as prey items. Their low pop-
ulation numbers, their ability to blend with the environment and their low palatability are the fea-
tures making them an unsuitable option for predators. Five individuals of the Patagonian seahorse
Hippocampus patagonicus were found in the stomach of a single narrownose smooth-hound shark
Mustelus schmitti from a sample of 959 stomachs analyzed. This rare record in a single stomach out
of hundreds analyzed suggests that these individuals might have clustered in a group which was
detected by the opportunistic M. schmitti.
Key words: Crypsis, diet, ‘El Rincón’, Syngnathidae, Triakidae.
Registro inusual de depredación múltiple del caballito de mar patagónico Hippocampus pata-
gonicus por el tiburón gatuzo Mustelus schmitti en aguas costeras argentinas
RESUMEN. Los caballitos de mar (Género Hippocampus) raramente son reportados como pre-
sas. Su baja densidad poblacional, su habilidad para confundirse entre su entorno y su baja palata-
bilidad son características que los hacen una opción poco atractiva para depredadores. Cinco indi-
viduos del caballito de mar patagónico Hippocampus patagonicus fueron encontrados en un único
estómago del análisis de una muestra de 959 estómagos del tiburón gatuzo Mustelus schmitti. Este
inusual registro en un solo estómago de los cientos analizados sugiere que los caballitos de mar se
encontraban agrupados cuando fueron detectados por el tiburón de hábitos oportunistas M. schmitti.
Palabras clave: Cripsis, dieta, “El Rincón”, Syngnathidae, Triakidae.
Sharks often play a role in the transfer of energy between trophic levels
within marine ecosystems. The diet composition of sharks has been studied
in order to understand the natural history of a particular species, their role in
marine ecosystems, the impact of shark predation on economically valuable
or endangered prey, among other reasons (Wetherbee and Cortés 2004).
269
*Correspondence:
diegoluzzatto@conicet.gov.ar
Received: 9 December 2020
Accepted: 9 February 2021
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
Marine and
Fishery Sciences
MAFIS
NOTE
Unusual record of a multiple predation of the Patagonian seahorse
Hippocampus patagonicus by the Narrownose smooth-hound Mustelus
schmitti in Argentine coastal waters
MAURO BELLEGGIA
1, 2, 3
, MARÍA G. PUJOL
4
, MARÍA L. ESTALLES
5
, DANIEL E. FIGUEROA
2, 6
and
DIEGO C. LUZZATTO
6, *
1
Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Paseo Victoria Ocampo Nº 1, Escollera Norte, B7602HSA - Mar del
Plata, Argentina.
2
Laboratorio de Biología de Peces, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata
(UNMdP), Funes 3350, B7602AYL - Mar del Plata, Argentina.
3
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET),
Argentina.
4
Museo Municipal de Ciencias Naturales “Lorenzo Scaglia”, Libertad 3099, B7600 - Mar del Plata, Argentina.
5
Instituto de
Formación Docente Continua - San Antonio Oeste, Islas Malvinas 1190, R8520 - San Antonio Oeste, Argentina.
6
Instituto de Investigaciones
Marinas y Costeras (IIMyC-CONICET), Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata (UNMdP),
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina
On their side, seahorses are rarely found as
prey items (Kleiber et al. 2011). Morphological
and ecological characteristics might contribute to
predator avoidance. These species exhibit a
remarkable capacity to be cryptic, they can
change their coloration pattern and some species
have long skin filaments or encrusting organisms
on the skin enabling them to blend with their
environments. They can remain virtually immo-
bile for a long time and occur at low densities,
which further complicates their localization (Fos-
ter and Vincent 2004). Their bony plates, spines
and low energetic value make them an unpalat-
able option for predators. In addition, in all the
cases recording seahorses as prey items, the pred-
ator has opportunistic and generalist habits
(Kleiber et al. 2011).
The Narrownose smooth-hound Mustelus
schmitti (Springer, 1939) is an opportunistic and
generalist benthic mesopredator. Its diet varies
along geographical locations and ontogeny and it
is mainly composed of fishes, crabs, isopods,
polychaetes, and mollusks (Belleggia et al. 2012).
The geographical range of this shark largely over-
laps with that of the Patagonian seahorse Hip-
pocampus patagonicus Piacentino and Luzzatto
2004 (Figure 1 A). Both species inhabit the coastal
areas of the Southwestern Atlantic Ocean extend-
ing from Rio de Janeiro (22° S, Brazil). However,
their southern limit differs. While M. schmitti
extends as south as Ria Puerto Deseado (47° 45′ S,
Argentina) mainly at depths below 140 m (Chiara-
monte and Pettovello 2000), H. patagonicus
extends up to Puerto Madryn (42° 47′ S, Argenti-
na) and has been described as occupying patches
in restricted areas at low depths mainly < 20 m
(Piacentino and Luzzatto 2004; Luzzatto et al.
2012; Silveira et al. 2014).
The Narrownose smooth-hound is the shark
most commonly caught by Argentinean fleets
(Sánchez et al. 2012). Heavy exploitation over its
entire geographical range (including nursery
areas), its decreasing biomass, declines in land-
ings, and reduction of size at first breeding have
all led to this species being considered Critical
Endangered by the International Union for Con-
servation of Nature (IUCN) Red List (Pollom et
al. 2020). The Patagonian seahorse is also a
threatened species and it is catalogued as Vulner-
able due to habitat degradation and overexploita-
tion (Wei et al. 2017). The present study reports
and describes a rare record of a multiple preda-
tion of the seahorse H. patagonicus by the shark
M. schmitti.
Sharks analyzed were collected during six bot-
tom-trawl research cruises conducted by the
research vessels ‘Doctor Eduardo L. Holmberg’,
‘Capitán Cánepa’, and ‘Capitán Oca Balda’ as
part of a study led by the Instituto Nacional de
Investigación y Desarrollo Pesquero (INIDEP)
during 2008-2011 (Belleggia 2012). These
research cruises were performed using a random
stratified sampling scheme (stratified on latitude
and depth; Figure 1 B). Surveys have been regu-
larly conducted by INIDEP in order to estimate
abundance. Fishing was conducted during day-
light hours (07:00-19:00), at 3 to 4 knots for 30
min at each sampling site using an Engel bottom
trawl (200 mm mesh in the wings, 103 mm in the
cod end, 4 m vertical opening and 15 m horizon-
tal opening). As part of a trophic ecology study,
we undertook research into the diet of M. schmitti
by sampling 959 individuals. Specimens of M.
schmitti were sexed and total length (TL) was
measured to the nearest mm from tip of the snout
to the posterior end of the dorsal caudal lobe in its
natural position. Maturity stage was recorded
according to Walker (2005) and Colonello et al.
(2011). Stomachs were excised, frozen and ana-
lyzed at the laboratory.
Prey items were identified to the lowest possi-
ble taxonomic level, counted and weighed to the
nearest 0.01 g. Diet composition was quantified
for each prey by calculating the percentage fre-
quency of occurrence (%F, total number of stom-
achs in which a given prey was found expressed
as percentage of total number of stomachs with
food), the percentage by number (%N, total num-
270
MARINE AND FISHERY SCIENCES 34 (2): 269-274 (2021)
ber of a given prey as percentage of total number
of prey found), percentage by mass (%M, mass of
a given prey as percentage of total mass of prey
found) and index of relative importance: IRI =
%F × (%N + %M) (Pinkas et al. 1971), expressed
as a percentage (%IRI; Cortés 1997).
A M. schmitti mature male of 652 mm TL and
1,052 g weight caught on research cruise ‘Capitán
Oca Balda’ in ‘El Rincón’ area (40.139° S-
61.436° W; 20 m depth) in April 2011 (Figure 1
B) contained five individuals of H. patagonicus
in different stages of digestion in its stomach.
One of the seahorses remained almost intact,
allowing several morphological measurements
(Figure 2 A). Another individual was partially
digested and some measurements were performed
(Figure 2 B). Both individuals were deposited in
the Syngnathid Collection of the Museum of Nat-
ural History ‘Lorenzo Scaglia’ (MMPEAA)
(Table 1). The other three individuals were
inferred by fragments of their tails and thoraxes.
No morphological measurements could be per-
formed on them.
Out of 959 specimens of M. schmitti analyzed
and 944 (98.43%) containing prey items, only
one contained seahorses. According to the index-
es estimated to quantify the diet composition of
M. schmitti, percentage of frequency of occur-
rence (%F) of seahorses in the diet was 0.01, per-
centage by number (%N) was 0.05, percentage by
weight (%W) was 0.02, and percentage of index
of relative importance (%IRI) was < 0.001.
Together with the five seahorses identified, this
stomach also contained other frequent prey items
for M. schmitti: shrimp Artemesia longinaris
(Bate, 1888) (0.04 g), brachyuran crabs Armases
rubripes Rathbun, 1897 (0.13 g) and Collodes
rostratus Edwards, 1878 (1.31 g, 14 mm), and
seven polychaetes of the families Ampharetidae
(0.33 g) and Onuphidae (0.21 g).
271
BELLEGGIA ET AL.: PREDATION OF THE PATAGONIAN SEAHORSE
Figure 1. A) Geographical range of Mustelus schmitti (blue) and Hippocampus patagonicus (red) in the Southwestern Atlantic.
Green square represents the study area. B) Study area indicating the position of bottom trawl samplings per date: October
2008 open dots, November 2008 bold dots, May 2009 open squares, September 2010 bold squares, April 2011 open tri-
angles, June 2011 bold triangles. Red asterisk indicates the sampling site (40.139° S- 61.436° W; 20 m depth) where the
specimen of M. schmitti presenting five individuals of H. patagonicus in its stomach was recorded.
Argentina
Uruguay
62° 61° 60° 59° 58° 57° 56° 55° 54° 53° 52° 51°
50 m 100 m 200 m
42°
41°
40°
39°
38°
37°
36°
35°
S
W
Atlantic Ocean
Southwest Atlantic
A
B
The record of patches of H. patagonicus at
shallow and intermediate depths (0-20 m) along
the coastal area of north Patagonia and Buenos
Aires Province and its record at deep waters (60
m) in the Uruguayan and Argentine Common
Fishing Zone (Luzzatto et al. 2012, 2014) indicat-
ed the presence of seahorses over a large depth
range. Juvenile specimens of H. patagonicus
drifting attached to floating debris or swimming
freely may interconnect the patches and facilitate
their ability to disperse to deep waters (Luzzatto
et al. 2013). The record presented here together
with that provided by Estalles et al. (2017) near
Monte Hermoso allow to infer the presence of the
species in an extended coastal area (Figure 1 B).
As it was indicated above, M. schmitti is an
opportunistic mesopredator shark. Its teeth are
similar in shape, arranged in semi-pavement like
crushing plates dentition, which makes it possible
for them to eat crabs, gastropods, bivalves and
other species protected by hard carapaces (Be-
lleggia et al. 2014). Bony plates, spines and other
morphological features of seahorses do not seem
to make them an unpalatable option for the shark.
However, this finding is the first record of sea-
horses in the diet composition of a Mustelus spp.
The predation event reported here is in line
with the general findings of seahorses as prey
items: their presence in the diet composition of
marine predators is infrequent and mainly con-
sisted of a single record. The presence of more
than one seahorse individual in a single stomach
is even rarer (Kleiber et al. 2011). The presence
of five seahorses in a single stomach out of hun-
272
MARINE AND FISHERY SCIENCES 34 (2): 269-274 (2021)
Figure 2. Measurable individuals of Hippocampus patagonicus obtained from the stomach of Mustelus schmitti. MMPEAA 36
(A) and MMPEAA 49 (B). Scale bar indicates 2 cm.
A
B
dreds analyzed suggests that these individuals
might have clustered in a group that was detected
by the opportunistic M. schmitti.
INIDEP contribution no 2240.
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Snout length (mm) 6 -
Dorsal fin base (mm) 7 4
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