An overview of the hooking mortality of elasmobranchs caught in a swordfish pelagic longline fishery in the Atlantic Ocean

Abstract

-Hooking (or "at-haulback") fishing mortality was analysed in elasmobranchs captured by Portuguese longliners targeting swordfish in the Atlantic Ocean. Information was collected by on-board fishery observers who monitored 834 longline fishing sets between August 2008 and December 2011, and recorded information on 36 067 elasmobranch specimens from 21 different taxa. The hooking mortality proportions were species-specific, with some species having relatively high percentages of live specimens at time of haulback (e.g., blue shark, crocodile shark, pelagic stingray, manta, devil and eagle rays), while others had higher percentages of dead specimens (e.g., smooth hammerhead, silky shark, bigeye thresher). For the most captured species (Prionace glauca, Pseudocarcharias kamoharai, Isurus oxyrinchus and Alopias superciliosus), logistic generalized linear models (GLMs) were carried out to compare the mortality rates between sexes, specimen sizes and the regions of operation of the fleet. The sex-specific proportions of hooking mortality were significantly different for blue and crocodile sharks, with the males of both species having higher proportions of hooking mortality than the females. Specimen size was significant for predicting the hooking mortality for blue and shortfin mako sharks: in both cases, the larger specimens had lower odds of dying due to the fishing process. There were differences in the hooking mortality depending on the region of operation of the fleet, but those differences were also species-specific. For blue and crocodile sharks, the hooking mortality was higher in the Equatorial and southern Atlantic areas (when compared to the NE Atlantic region), while the opposite was observed for the shortfin mako, with lower mortality rates in the NE tropical area compared with the other regions. The results presented in this paper can be integrated into future ecological risk assessment analysis for pelagic elasmobranchs. Furthermore, the new information can be used to evaluate the impact of recent recommendations prohibiting the retention of some vulnerable elasmobranch species.

Effects of leader material on catches of shallow pelagic longline fisheries in the southwest Indian Ocean

“…Although a relatively small number of specimens of other shark species were caught during our experi ment, the dead versus alive ratios (mortality at haul back) observed were consistent with those reported by Coelho et al (2012b) for a similar fishery in the Atlan tic Ocean. The exception was the shortfin mako, which in this case showed a much lower mortality ratio at haulback (7-15%).…”

“…Additionally, we should note that Campana et al (2015) used mainly circle hooks, whereas in our study we used J hooks that can affect the hooking location (mouth or jaw vs. deeply hooked) and consequently on the injuries of the discarded specimens. Apart from high mortality at haulback for many shark species (Coelho et al, 2012b), we also found high mortality rates at haulback with the use of nylon monofilament and wire leaders for commonly discarded species such as the longnose lancetfish (60% and 61%), and the snake mackerel (88% and 81%, respectively),…”

“…The exception was the shortfin mako, which in this case showed a much lower mortality ratio at haulback (7-15%). Coelho et al (2012b) reported a rela tionship between hooking mortality and specimen size for the shortfin mako in the Atlantic Ocean, with larger specimens having a lower probability of being dead at haulback. Because the size distribution in this region of the Indian Ocean tends to be composed of larger specimens than those in the Atlantic Ocean, as report ed by the Coelho et al (2012b) According to our results, there was not a significant difference in the VPUE, but it should be noted that our estimates were based on the average market price for a single month.…”

Transboundary movements, unmonitored fishing mortality, and ineffective international fisheries management pose risks for pelagic sharks in the Northwest Atlantic

“…Sharks are usually discarded. Hooking mortality rates differ across species, fishing fleet, fisher, and water temperatures, but porbeagles, shortfin makos, and blue sharks caught by pelagic longlines in the North Atlantic experience hooking mortality rates of 15%-44% (Mandelman et al 2008;Coelho et al 2012;Campana et al 2016). Is this any different from hooking mortality rates for comparably sized teleosts?…”

Fisheries Bycatch of Chondrichthyes

“…Notably, blue shark (Prionace glauca) is the most encountered bycatch species in pelagic longline fisheries mainly around sub-tropical and temperate regions [5,25]. This species is currently listed as Near Threatened globally, while as Critically Endangered in Europe and Mediterranean [26].…”