A century of fishery data documenting the collapse of smooth‐hounds (Mustelus spp.) in the Mediterranean Sea

1. Conservation and management of shark populations is increasingly becoming important in many marine regions, since there is a growing body of evidence showing that several species are threatened and continuing to decline because of unregulated fishing. Quantifying the extent of sharks' decline, the risk of species extinction, and the consequences for marine ecosystems have been challenging and controversial, mostly due to data limitations.
2. In this study, more than one century of multiple‐sources of bibliographic records on presence and frequency of occurrence of three species of commercial sharks, the smooth‐hounds Mustelus spp., in the Mediterranean Sea were compiled and analysed. Generalized additive models for location, scale and shape (GAMLSS) were used to estimate the rate of change of two of these species, Mustelus mustelus and Mustelus punctulatus, in four Mediterranean regions.
3. Model results showed that smooth‐hounds have declined by 80–90% since the beginning of last century to almost disappear in a large part of their original distributional range during the 1980s and 1990s.
4. Based on modelling results, a revision of the current International Union for Conservation of Nature classification of Mediterranean smooth‐hounds would be advisable along with the application of urgent conservation measures.

     

Preliminary recovery of coastal sharks in the south‐east United States

Relative abundance of many shark species in the Atlantic is assessed by compiling data from several independently conducted, but somewhat spatially limited surveys. Although these localized surveys annually sample the same populations, resulting trends in yearly indices often conflict with one another, thereby hindering interpretation of abundance patterns at broad spatial scales. We used delta‐lognormal generalized linear models (GLMs) to generate indices of abundance for seven Atlantic coastal shark species from six fishery‐independent surveys along the US east coast and Gulf of Mexico from 1975 to 2014. These indices were further analysed using dynamic factor analysis (DFA) to produce simplified, broad‐scale common trends in relative abundance over the entire sampled distribution. Effects of drivers including the North Atlantic Oscillation index, the Atlantic Multidecadal Oscillation index, annually averaged sea surface temperature and species landings were evaluated within the DFA model. The two decadal oscillations and species landings were shown to affect shark distribution along south‐east US coast. Estimated common trends of relative abundance for all large coastal shark species showed similar decreasing patterns into the early 1990s, periods of sustained low index values thereafter and recent indications of recovery. Small coastal shark species exhibited more regional variability in their estimated common trends, such that two common trends were required to adequately describe patterns in relative abundance throughout the Gulf of Mexico and Atlantic. Overall, all species’ (except the Gulf of Mexico blacknose shark) time series concluded with an increasing trend, suggestive of initial recovery from past exploitation.     

The sharks of South East Asia – unknown,unmonitored and unmanaged

Sharks fisheries have declined globally due to over‐ and unregulated fishing. As with many collapsed and unmonitored coastal fisheries, information is difficult to obtain, yet it is important to understand the historical changes determining population trends and evaluate the current status of sharks in order to conserve these vulnerable species. Here, we document for the first time the history and general condition of the shark fisheries of Southern China, specifically Hong Kong, and Guangdong, Fujian and Hainan Provinces. This study shows, through the use of historical literature and anecdotal accounts, including fisher interviews, that all known shark fisheries in the region collapsed between the 1970s and the 1990s. Of the 109 species present historically in the South China Sea, only 18 species were recorded in current market surveys, of which all were landed as bycatch and 65% were below the size of sexual maturity. Markets are dominated by smaller species, including the spadenose shark (Scoliodon laticaudus) and the whitespotted bambooshark (Chiloscyllium plagiosum). Marketed large shark species are almost all below the size of sexual maturation, evidence of growth overfishing and a factor in recruitment overfishing. Some species, like the whale (Rhincodon typus) and basking sharks (Cetorhinus maximus), are clearly vulnerable to local extinction without intervention. Given the inherent vulnerability of sharks and the overfished states of many sharks, there is clearly an urgent need to formulate impacting conservation and management plans for these rapidly declining species in a region that has the highest demand for shark products globally.     

Using fishers’ ecological knowledge to assess the status and cultural importance of sawfish in Guinea‐Bissau

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Melanomacrophages in three species of free-ranging sharks from the northwestern Atlantic, the blue shark Prionacae glauca (L.), the shortfin mako, Isurus oxyrhinchus Rafinesque, and the thresher, Alopias vulpinus (Bonnaterre)

The melanomacrophage aggregates or cells (MMC) are commonly used as biomarkers of exposure to pollution in fish, albeit their numbers and morphological characteristics can be influenced not only by environmental toxins but also by a range of physiological parameters and pathological conditions. Accordingly, before we can use MMC as biomarkers in any fish species, their normal, 'background' characteristics have to be established in apparently healthy fish. The knowledge of MMC in sharks is minimal. The aim of this study was to characterize MMC from 51 free-ranging, large pelagic sharks from the northwestern Atlantic, including shortfin mako, Isurus oxyrhinchus , thresher, Alopias vulpinus and blue shark, Prionacae glauca . The rationale of this study was twofold. First, because, sharks have life histories predisposing them to the accumulation of environmental toxins they constitute good sentinel species of the health of the global marine ecosystem. Second, because many shark populations are in decline or threatened by extinction, we need to expand our understanding of their health status in order to develop appropriate protective measures. All sharks were collected by sports fishing gear between June and August in 2007. Their health condition was assessed by necropsy, morphometrics, and by microscopic examination of gonads, livers, spleens and kidneys. Routine, haematoxylin and eosin and/or Pearl's reagent-stained paraffin embedded sections were studied by light microscopy. Our results provide the first data on the morphometric and morphological characteristics of MMC in viscera of apparently healthy free-ranging sharks from the northwestern Atlantic.     

Are circle hooks effective management measures in the pelagic longline fishery for sharks in the Gulf of Gabès?

1. This study evaluated the circle hook use as a tool for shark management in the pelagic longline fishery in the Gulf of Gabès.
2. The usual J‐hook No. 2 with 10° offset, which has been traditionally used by the fishery, was compared to the 18/0 non‐offset circle hook in an alternating fashion along the main line. In total, 22 experimental longline sets were deployed through the shark fishing seasons of 2016 and 2017 to examine the effects of hook types on the catch composition, the catch rates, the hooking location, and the status at haulback.
3. The catch composition differed significantly among hook types. Moreover, an overall increase in catch rates for the main species, the sandbar shark Carcharhinus plumbeus, and the shortfin mako shark Isurus oxyrinchus, was observed when using circle hooks.
4. There was no size‐selective effect of circle hooks for the common species. The circle hooks were not effective at reducing at‐haulback mortality of sandbar shark. Conversely, shortfin mako and smooth‐hound shark Mustelus mustelus showed significantly lower relative mortality at haulback with circle hooks than with J‐hooks. Furthermore, circle hooks were more frequently hooked externally than the J‐hooks for the three shark species.
5. Results demonstrated that the use of 18/0 non‐offset circle hooks in the pelagic shark longline fishery can reduce mortality at haulback for some species without any benefit for the dominant species, the sandbar shark.
6. Overall, it is difficult to promote the adoption of the use of circle hooks as a management measure in this specialized fishery. Management measures focusing on fishing effort controls, fishing closures in critical habitats, and size limits could have significant benefits for the conservation of shark species and may help to improve the sustainability of the shark fishery in the Gulf of Gabès.

     

东太平洋金枪鱼延绳钓兼捕鲨鱼种类及其渔获量分析

2003年7月-11月份期间,对东太平洋公海海域(03°S~17°S,96°W~146°W)的超低温金枪鱼延绳钓兼捕鲨鱼进行调查。发现共兼捕到9种鲨鱼,分别是尖吻鲭鲨、长鳍鲭鲨、鳄鲨、人眼长尾鲨、路氏双鲨、长鳍真鲨、镰状真鲨、大青鲨和黑异鳞鲨,隶属于3目6科。共钓获鲨鱼24 711 kg,其中大青鲨是优势种类,占鲨鱼渔获尾数的50.4%,占鲨鱼渔获总重量的76.5%,平均个体重量达到64.9 kg。调查获得9种大洋性鲨鱼的渔获率,其中以大青鲨的最高,达到0.964尾数/千钩,鳄鲨次之为0.497尾数/千钩,其它鲨鱼的CPUE均在0.200尾数/千钩以下,此外估计了东太平洋海域金枪鱼延绳钓兼捕鲨鱼总渔获量,约在4.0~5.9万吨。     

Molecular species identification and population genetics of chondrichthyans in South Africa: current challenges,priorities and progress

Molecular genetic techniques, such as DNA barcoding and genotyping, are increasingly being used to assist with the conservation and management of chondrichthyans worldwide. Southern Africa is a shark biodiversity hotspot, with a large number of endemic species. According to the IUCN Red List, a quarter of South Africa's chondrichthyans are threatened with extinction. South Africa's commercial shark fisheries have increased over the last decade and there is a need to ensure sustainable utilisation and conservation of this fisheries resource. Here, we give an overview of the molecular techniques that are used to assist in the identification of species, cryptic speciation and possible interspecific hybridisation, as well as the assessment of population structure and reproductive behaviour of endemic and commercially important chondrichthyan species of southern Africa. We discuss the potential application of these techniques for management and conservation of several species affected by South African fisheries. Acquiring baseline barcode data of all chondrichthyans in southern African waters and assessing the population structure of exploited species on a local and greater regional scale are recommended as research priorities. Future prospects should also include high-throughput molecular marker development and investigation of intraspecies functional variation using next generation sequencing technology.     

Fishery indicators during a predictable aggregation of Atlantic sharpnose sharks Rhizoprionodon terraenovae in the southern Gulf of Mexico: An alternative to assess a heterogeneous data‐poor fishery

Small‐scale fisheries in the southern Gulf of Mexico that catch Rhizoprionodon terraenovae (Richardson) are heterogeneous and data‐poor. Fishery‐dependent monitoring was conducted from 2010 to 2017, including a target season during an aggregation of this species to estimate data‐poor fishery indicators. During the target season, the average sizes for females and males (95.3 and 89.8 cm total length, respectively) were recorded, a global male sex bias (1:1.7), the highest percentage of mature sharks for all years (>89%), the highest values of CPUE (20.1 sharks/day) and size‐selectivity higher than the size at maturity. The spawning potential ratio was over 0.6 (reference point of 0.71) in the combined (target and non‐target) and target seasons for all years, which suggests that the fishery stock is not healthy. Annual assessment of this fishery can be carried out through monitoring during the target season, where management is more feasible to implement.     

Basking sharks (Cetorhinus maximus) schooling in the southern Gulf of Maine

Schools of up to 50 basking sharks (Cetorhinus maximus) were observed on the warm side of a persistent thermal front in the southern Gulf of Maine from early September through mid‐October 2002. Aerial photographs showed a variety of schooling patterns, including echelon, cartwheel and milling formations. While the function of these aggregations remains unknown, they may represent group courtship behaviour.