Combined stomach content and δ¹³C/δ¹⁵N analyses of oilfish, escolar, snake mackerel and lancetfish in the western North Atlantic

Abstract

Large, mesopelagic teleost fishes have a potentially keystone position in the ecology of the pelagic water column, yet remain relatively unstudied when compared with large, commercially important, epipelagic fishes. Here, the ecological roles of four, large, vertically migrating teleosts were examined. Stomach content analyses were performed on 48 oilfish (Ruvettus pretiosis), 35 escolar (Lepidocybium flavobrunneum), 32 snake mackerel (Gempylus serpens) and seven lancetfish (Alepisaurus spp.) collected from pelagic longline gear in the Western North Atlantic Ocean from 2007 to 2010. Of these specimens, stable carbon and nitrogen isotope analyses were also performed on white dorsal muscle tissue from 33 oilfish, 16 escolar, 27 snake mackerel and seven lancetfish. Based on literature length-at-maturity values, all escolar, snake mackerel and lancetfish specimens were mature, while 13 of the 33 oilfish were juveniles. Crustaceans, annelids, salps, cephalopods and teleosts were present in the stomachs and were presumed to be prey items. A Kruskal-Wallis test showed the four species to be isotopically segregated in both d 13 C and d 15 N. Escolar were the most depleted in d 13 C, followed by adult oilfish, juvenile oilfish and lancetfish, with snake mackerel the most enriched. The depletion in d 13 C of adult oilfish and escolar may have been attributable to high C/N values, which were strongly correlated with length in oilfish, weakly correlated with length in escolar and moderately correlated with length in snake mackerel and lancetfish. The high C/N was likely due to the high lipid concentration of these fishes. Other factors that may have contributed to the depletion in d 13 C may include spawning or a change in carbon source within the ecosystem. Large escolar occupied the highest trophic level (d 15 N = 10.20), followed by snake mackerel (d 15 N = 9.66), adult oilfish (d 15 N = 9.32), lancetfish (d 15 N = 9.05) and juvenile oilfish (d 15 N = 7.83). A marked change in oilfish d 13 C and C/N at 30-35 cm fork length coincided with a presumed length-at-maturity.

Preliminary assessment of the trophic structure of demersal fish community in the Sea of Oman

“…Our results therefore highlight how essential insights from stable isotope analysis had proven to complement stomach content data, in order to fully apprehend the variability in feeding habits of consumers. Similar conclusions have been presented by recent studies (Carassou et al, 2016 andKeller et al, 2016;Olson et al, 2016). Stomach contents indeed only provide very short-term information on consumer's diet, while isotopic ratios in the tissues reflect dietary habits over longer time scales (Cortés, 1997;Hobson, 1999;Post, 2002;Olson et al, 2016).…”

“…In this context, stable isotopes of carbon ( 13 C/ 12 C, or δ 13 C) and nitrogen ( 15 N/ 14 N, or δ 15 N) are the most often measured in food web studies (Hobson, 1999;Post, 2002). The combination of stomach content with δ 13 C and δ 15 N analyses is now recognized as a pertinent methodology in order to quantify fish diet and address its spatial and temporal variability in a given ecosystem (Hamidan et al, 2016;Keller et al, 2016;Malek et al, 2016;Olson et al, 2016;Weidner et al, 2017). In addition to carbon and nitrogen isotopic ratios, sulfur isotopes are also useful to trace the origin of the prey consumed by consumers in aquatic ecosystems (Peterson, 1999;Post, 2002;Fry and Chumchal, 2011).…”

Combined gut-content and stable isotope trophic analysis of the pelagic stingray Pteroplaytrygon violacea (Bonaparte, 1832) diet from the western North Atlantic Ocean

“…The stable isotope values were then compared to literature values for potential prey; additional pelagic fish species’ δ 13 C and δ 15 N were used due to the logistical difficulties associated with physically collecting some specimens (e.g., small pelagic shrimp, squid species, isopods) while aboard the cooperating commercial pelagic longline fishing vessels. Several studies have already reported values for some prey items, such as Atlantic herring, pelagic squids, and Atlantic flying fishes (e.g., Estrada et al., ; Rau et al., ), or co‐occurring predators, such as mesopelagic fishes (Keller, Hirons, & Kerstetter, ).…”