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Historical trophic ecology of some divergent shark and skate species in the Dutch coastal North Sea zone

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Over the last century the fish community of the Dutch coastal North Sea zone has lost most its shark and skate species. Whether their disappearance has changed the trophic structure of these shallow waters has not been properly investigated. In this study historical dietary data of sharks and skates, being in the past (near)-residents, juvenile marine migrants and marine seasonal visitors of the Dutch coastal North Sea zone were analyzed for the period 1946-1954. Near-resident and juvenile marine migrant species were demersal while all marine seasonal visitors species were pelagic. Based on stomach content composition, the trophic position of four of the various shark and skate species could be reconstructed. The (near)-resident species, the lesser spotted dogfish, the marine juvenile migrant, the starry smooth hound, and the benthopelagic marine seasonal visitor, the thornback ray, had a benthic/demersal diet (polychaetes, molluscs and crustaceans), while the pelagic marine seasonal visitor, the tope shark, fed dominantly on cephalopods and fishes. Diet overlap occurred for fish (tope shark and lesser spotted dogfish), for hermit crabs (lesser spotted dogfish and starry smooth hound) and for shrimps (thornback ray and starry smooth hound). Trophic position ranged from 3.2 for thornback ray preying exclusively on crustaceans to 4.6 for the tope shark consuming higher trophic prey (crustaceans and fish). The analysis indicates that most of the shark and skate species were generalist predators. The calculated trophic positions of shark and skate species indicate that those species were not necessarily at the top of the marine ecosystem food web, but they might have been the top predators of their particular ecological assemblage.
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Marine Biology (2021) 168:165
https://doi.org/10.1007/s00227-021-03974-0
ORIGINAL PAPER
Historical trophic ecology ofsome divergent shark andskate species
intheDutch coastal North Sea zone
SuzanneS.H.Poiesz1,2 · TomasvanElderen1· JohannesIJ.Witte1· HenkW.vanderVeer1
Received: 29 October 2020 / Accepted: 30 September 2021 / Published online: 22 October 2021
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021
Abstract
Over the last century the fish community of the Dutch coastal North Sea zone has lost most its shark and skate species.
Whether their disappearance has changed the trophic structure of these shallow waters has not been properly investigated. In
this study historical dietary data of sharks and skates, being in the past (near)-residents, juvenile marine migrants and marine
seasonal visitors of the Dutch coastal North Sea zone were analyzed for the period 1946–1954. Near-resident and juvenile
marine migrant species were demersal while all marine seasonal visitors species were pelagic. Based on stomach content
composition, the trophic position of four of the various shark and skate species could be reconstructed. The (near)-resident
species, the lesser spotted dogfish, the marine juvenile migrant, the starry smooth hound, and the benthopelagic marine
seasonal visitor, the thornback ray, had a benthic/demersal diet (polychaetes, molluscs and crustaceans), while the pelagic
marine seasonal visitor, the tope shark, fed dominantly on cephalopods and fishes. Diet overlap occurred for fish (tope shark
and lesser spotted dogfish), for hermit crabs (lesser spotted dogfish and starry smooth hound) and for shrimps (thornback
ray and starry smooth hound). Trophic position ranged from 3.2 for thornback ray preying exclusively on crustaceans to 4.6
for the tope shark consuming higher trophic prey (crustaceans and fish). The analysis indicates that most of the shark and
skate species were generalist predators. The calculated trophic positions of shark and skate species indicate that those spe-
cies were not necessarily at the top of the marine ecosystem food web, but they might have been the top predators of their
particular ecological assemblage.
Keywords Historical trophic ecology· Dutch coastal North Sea zone· Food web reconstruction· Historical dietary data·
Predator–prey interactions· Sharks and rays· Trophic positions
Introduction
Worldwide, major structural and functional changes have
occurred in coastal ecosystems due to overfishing (Pauly
etal 1998; Jackson etal 2001; Lotze 2005). Pauly etal
(1998) state that this so-called “fishing down the marine
food web” reflects the removal of long-lived, high trophic
level, piscivorous fish, including sharks and skates. It is
unclear what effect the removal of top predators can have
on the stability of a community (Shurin etal 2002), because
for instance the relationship between food chain stability
and food chain length is unclear (Sterner etal 1997). While
it is easy to predict that carnivores have a high trophic posi-
tion and exert a degree of top-down effects, these effects are
still very poorly understood (Cortés 1999). Consequences
of the removal of top predators could have a cascading
effect down the food web, through to lower trophic posi-
tions such as bivalves and polychaetes (Hussey etal 2015).
These cascades potentially could extend to the level of the
primary producers (Myers etal 2007). Considering these
possible consequences, eliminating larger predators carries
more risks of broader ecosystem degradation than previously
thought. Top down effects must be widely expected when-
ever entire groups of predators are eliminated or removed.
Responsible Editor: C. Harrod.
* Suzanne S. H. Poiesz
suzanne.poiesz@nioz.nl
1 Department ofCoastal Systems, NIOZ Royal Netherlands
Institute forSea Research, Den Burg, P.O. Box59,
1790ABTexel, TheNetherlands
2 Faculty ofScience andEngineering, Groningen Institute
ofEvolutionary Life Sciences, University ofGroningen,
P.O. Box11103, 9700CCGroningen, TheNetherlands
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Predatory shark and skate species had TPs (based on historical archive dietary data) in the range of 3.2−4.6 (Poiesz et al. 2021). Another explanation might be due to trophic downgrading, where food webs lose complexity and trophic biodiversity due to changing environmental conditions (changing temperatures, eutrophication) and competition (Saleem 2015, Edwards & Konar 2020, Yan et al. 2020). ...
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