Environmental factors and megafauna spatio‐temporal co‐occurrence with purse‐seine fisheries

Tropical tuna purse‐seine fisheries spatially co‐occur with various megafauna species, such as whale sharks, dolphins and baleen whales in all oceans of the world. Here, we analyzed a 10‐year (2002–2011) dataset from logbooks of European tropical tuna purse‐seine vessels operating in the tropical Eastern Atlantic and Western Indian Oceans, with the aim of identifying the principle environmental variables under which such co‐occurrence appear. We applied a Delta‐model approach using Generalized Additive Models (GAM) and Boosted Regression Trees (BRT) models, accounting for spatial autocorrelation using a contiguity matrix based on a residuals autocovariate (RAC) approach. The variables that contributed most in the models were chlorophyll‐a concentration in the Atlantic Ocean, as well as depth and monsoon in the Indian Ocean. High co‐occurrence between whale sharks, baleen whales and tuna purse‐seine fisheries were mostly observed in productive areas during particular seasons. In light of the lack of a full coverage scientific observer on board program, the large, long‐term dataset obtained from logbooks of tuna purse‐seine vessels is highly important for identifying seasonal and spatial co‐occurrence between the distribution of fisheries and megafauna, and the underlying environmental variables. This study can help to design conservation management measures for megafauna species within the framework of spatial fishery management strategies.     

When large marine predators feed on fisheries catches: Global patterns of the depredation conflict and directions for coexistence

The sustainable mitigation of human–wildlife conflicts has become a major societal and environmental challenge globally. Among these conflicts, large marine predators feeding on fisheries catches, a behaviour termed “depredation,” has emerged concomitantly with the expansion of the world’s fisheries. Depredation poses threats to both the socio‐economic viability of fisheries and species conservation, stressing the need for mitigation. This review synthesizes the extent and socio‐ecological impacts of depredation by sharks and marine mammals across the world, and the various approaches used to minimize it. Depredation was reported in 214 fisheries between 1979 and 2019 (70% post‐2000) and affected fleets from 44 countries, in all sectors (commercial, artisanal and recreational), and in all major fishing techniques (nets, traps and hook‐and‐lines). A total of 68 predator species were involved in depredation (20 odontocetes, 21 pinnipeds and 27 sharks), and most (73%) were subject to either by‐catch and/or retaliatory killing from fishers when interacting with gear. Impacts on fishers were primarily associated with catch losses and gear damage but often lacked assessments. Deterrence was a major mitigation approach but also the least effective. Gear modifications or behavioural adaptation by fishers were more promising. This review highlights the need for improved monitoring, and interdisciplinary and integrated research to quantify the determinants and impacts of depredation in the socio‐ecological dimension. More importantly, as the conflict is likely to escalate, efforts directed towards changing perceptions and integrating knowledge through adaptive co‐management are raised as key directions towards coexistence between fisheries and large marine predators.     

Protein mining the world's oceans: Australasia as an example of illegal expansion-and-displacement fishing

Illegal, unreported and unregulated (IUU) fishing can lead to irreversible ecosystem changes; however, it is also one of the most difficult forms of fishing to manage and deter. In northern Australia over the past decade there has been a large increase in small-scale IUU fishing. We suggest that this small-scale fishing has arisen because of long-term fisheries over-exploitation in South East Asia. This IUU fishing forms part of the expansion-and-displacement cycle that can rapidly reduce biomass and alter the trophic structure of local ecosystems. With increasing human populations in the region, the pressure to fish illegally is likely to increase. Regional responses are required to deter and monitor the illegal over-exploitation of fisheries resources, which is critical to secure ecosystem stability as climate change and other destructive human activities threaten food security.     

Comparing GLM,GLMM, and GEE modeling approaches for catch rates of bycatch species: A case study of blue shark fisheries in the South Atlantic

Modeling and understanding the catch rate dynamics of marine species is extremely important for fisheries management and conservation. For oceanic highly migratory species in particular, usually only fishery‐dependent data are available which have limitations in the assumption of independence and if often zero‐inflated and/or overdispersed. We tested different modeling approaches applied to the case study of blue shark in the South Atlantic, by using generalized linear models (GLMs), generalized linear mixed models (GLMMs), and generalized estimating equations (GEEs), as well as different error distributions to deal with the presence of zeros in the data. We used fractional polynomials to deal with non‐linearity in some of the explanatory variables. Operational (set level) data collected by onboard fishery observers, covering 762 longline sets (1,014,527 hooks) over a 9‐year period (2008–2016), were used. One of the most important variables affecting catch rates is leader material, with increasing catches when wire leaders are used. Spatial and seasonal variables are also important, with higher catch rates expected toward temperate southern waters and eastern longitudes, particularly between July and September. Environmental variables, especially SST, also affect catches. There were no major differences in the parameters estimated with GLMs, GLMMs, or GEEs; however, the use of GLMMs or GEEs should be more appropriate due to fishery dependence in the data. Comparing those two approaches, GLMMs seem to perform better in terms of goodness‐of‐fit and model validation.     

淡水鲨鱼养殖生物学特性和健康养殖技术

介绍淡水鲨鱼的形态特征、生活习性、生长、繁殖等生物学特性,以及淡水鲨鱼温流水养殖、混养模式和科学用药等健康养殖技术。     

Report card on ecosystem‐based fisheries management in tuna regional fisheries management organizations

International instruments of fisheries governance have set the core principles for the management of highly migratory fishes. We evaluated the progress of tuna Regional Fisheries Management Organizations (tRFMOs) in implementing the ecological component of ecosystem‐based fisheries management (EBFM). We first developed a best case tRFMO for EBFM implementation. Second, we developed criteria to evaluate progress in applying EBFM against this best case tRFMO. We assessed progress of the following four ecological components: target species, bycatch species, ecosystem properties and trophic relationships, and habitats. We found that many of the elements necessary for an operational EBFM are already present, yet they have been implemented in an ad hoc way, without a long‐term vision and a formalized plan. Overall, tRFMOs have made considerable progress monitoring the impacts of fisheries on target species, moderate progress for bycatch species, and little progress for ecosystem properties and trophic relationships and habitats. The tRFMOs appear to be halfway towards implementing the ecological component of EBFM, yet it is clear that the “low‐hanging fruit” has been plucked and the more difficult, but surmountable, issues remain, notably the sustainable management of bycatch. All tRFMOs share the same challenge of developing a formal mechanism to better integrate ecosystem science and advice into management decisions. We hope to further discussion across the tRFMOs to inform the development of operational EBFM plans.     

Shark reactions to scuba divers in two marine protected areas of the Eastern Tropical Pacific

• 1. Worldwide, there are concerns about the potential impact of a growing tourism industry on the behaviour and ecology of sharks. Several shark species are key attractions in the scuba diving industry in both the Galápagos Marine Reserve (Ecuador) and the Sanctuary of Fauna and Flora Malpelo (Colombia).
• 2. In this study, the reactions of five species of shark to the behaviour of scuba divers were investigated in the Galápagos and Malpelo.
• 3. Four discrete categories of shark reaction (evasion, spontaneous approach, alert and no reaction) were identified and analysed against five categories of diver behaviour (direct approach, camera flash, sudden movement, noise and simple presence), two categories of observation strategy (still and movement) and the distance of the focal diver group to the sharks.
• 4. The type of reaction in the sharks was determined by the behaviour of the divers, their distance to the fish and, especially, by their observation strategy. Shark reactions varied between species and locations and divers acted more intrusively towards those species they were not afraid of, and which they could access more easily due to the conditions of their environment.
• 5. ‘Direct approach’, ‘sudden movement’, the observation strategy ‘moving’ and distances closer than 4 m between divers and sharks elicited stronger behavioural responses by the species targeted. Recommendations are given for the preferred actions divers should employ in order to diminish the effects on the target species analysed in this study. Copyright © 2011 John Wiley & Sons, Ltd.

     

Mortality due to a retained circle hook in a longfin mako shark Isurus paucus (Guitart‐Manday)

A female longfin mako shark Isurus paucus (Guitart‐Manday, 1966) was found moribund on the Atlantic Ocean beach near Canaveral National Seashore, Florida; the shark died shortly after stranding. Macroscopic lesions included a partially healed bite mark on the left pectoral fin, a clefted snout, pericardial effusion and a pericardial mass surrounding a 12/0 circle fishing hook. The heart, pericardial mass, gills, ovary, oviduct, shell gland, epigonal organ, liver, kidney and intrarenal and interrenal glands were processed for histopathology and examined by brightfield microscopy. Microscopic examination revealed chronic proliferative and pyogranulomatous pericarditis and myocarditis with rhabdomyolysis, fibrosis and thrombosis; scant bacteria and multifocal granular deposits of iron were found intralesionally. In addition, acute, multifocal infarcts within the epigonal organ and gill filaments were found in association with emboli formed by necrocellular material. The ovary had high numbers of atretic follicles, and the liver had diffuse, severe hepatocellular degeneration, multifocal spongiosis and moderate numbers of melanomacrophage cells. This report provides evidence of direct mortality due to systemic lesions associated with retained fishing gear in a prohibited shark species. Due to the large numbers of sharks released from both recreational and commercial fisheries worldwide, impact of delayed post‐release mortality on shark populations is an important consideration.