Naturally occurring lesions and micro-organisms in two species of free-living sharks: the spiny dogfish, Squalus acanthias L., and the smooth dogfish, Mustelus canis (Mitchill), from the north-western Atlantic

Twenty-three smooth dogfish, Mustelus canis L., and 20 spiny dogfish, Squalus acanthias (Mitchill), were examined for the presence of diseases. Sharks were collected from the north-western Atlantic between April and September 2000. Major organs were sampled for histopathology and bacterial cultures were taken from kidneys. Macroscopic lesions were infrequent and included intestinal cestodiasis and gastric and dermal erosions. Microscopic lesions were common in both shark species. Mustelus canis had numerous degenerative lesions involving the pancreatic ducts, seminiferous tubules and coronary vessels. The most frequent lesions in S. acanthias were parasitic and included pancreatic nematodiasis and biliary myxosporeosis. Additionally, both species had focal meningitis, encephalitis, dermatitis, gastritis, enteritis and glomerulomesangial thickening. Microscopic parasites included intestinal coccidiosis, unclassified gastric and testicular protozoa, skeletal muscle and renal tubular myxosporeans, a branchial trichodinid ciliate, olfactory and branchial trematodes, gastrointestinal cestodes and larval nematodes. Shewanella putrefaciens , Photobacterium sp., Vibrio sp., Pseudomonas sp. and Alteromonas sp. were isolated from kidneys of nine sharks. The role of the above lesions in the natural mortality and morbidity of the two shark species is unknown. The finding that apparently healthy sharks can harbour potentially debilitating lesions warrants the inclusion of histopathological studies in the management and conservation of sharks.     

Comparison of histological features, and description of histopathological lesions in thyroid glands from three species of free-ranging sharks from the northwestern Atlantic, the blue shark, Prionace glauca (L.), the shortfin mako, Isurus oxyrhinchus Rafinesque, and the thresher, Alopias vulpinus (Bonnaterre)

Histomorphological features of piscine thyroids are widely accepted and frequently used as bioindicators of environmental pollution. This despite the fact that there is marked variation in thyroid morphology resulting from numerous pathological and physiological conditions. Our hypothesis was that there will be variations in histological features in thyroids collected from different shark species during the summer season in the northwestern Atlantic. To test our hypothesis, we examined histological features encountered in grossly normal thyroids from three species of sharks, the shortfin mako, Isurus oxyrhinchus , thresher, Alopias vulpinus and blue sharks, Prionace glauca . In addition, microscopic lesions from these thyroids were described. Ninety-four sharks were collected in summer 2001, 2002 and 2004. Routine, haematoxylin and eosin-stained paraffin-embedded sections were studied by light microscopy. We found inter-species but not intra-species variation in histological patterns of thyroids, which were distinct enough to allow 'blind' assignment of a thyroid to the specific species. The most common lesions encountered were lymphofollicular hyperplasia and chronic thyroiditis. In addition, one case each of intravascular larval nematodes and a myxosporean infection was found. Our results provide the first data on species-specific morphology of thyroids collected during summer months from sharks. The results indicate that familiarity with normal thyroid morphology is crucial before using shark thyroids in biomonitoring of environmental contamination or interpreting data from this gland in shark-health studies.     

Mode of attachment and lesions associated with trypanorhynch cestodes in the gastrointestinal tracts of two species of sharks collected from coastal waters of Borneo

Lesions associated with two species of tapeworms within the digestive tract of wild-caught specimens of the bull shark, Carcharhinus leucas, and the sicklefin weasel shark, Hemigaleus microstoma, from Malaysian Borneo are described. Portions of the glandular stomach and pyloric gut with parasites were removed and fixed in 10% formalin buffered in sea water. Whole mounts, histological sections of tissues with and without worms in situ, and scanning electron microscopy images of detached worms were examined. Both species of cestodes belonged to the trypanorhynch family Tentaculariidae. Heteronybelinia estigmena was found in large numbers parasitizing the pyloric gut of C. leucas; an unidentified tentaculariid was found in relatively small numbers in both the glandular stomach and pyloric gut of H. microstoma. Both species burrowed their scoleces deeply in the mucosa and attached via hooked tentacles and unciniform microtriches of the scolex. The lesions induced by the parasites were marked in both sharks and ranged from acute necrotizing to chronic granulomatous gastroenteritis. Regenerative hyperplasia and intestinal metaplasia of gastric epithelium were also present. The severity and character of pathology was causally linked to the intensity of infection, the attachment mode of the parasites, and to the anatomophysiological relationships within the gut of the host shark.     

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.     

Pathology associated with retained fishing hooks in blue sharks, Prionace glauca (L.), with implications for their conservation

Fishing hooks retained from previous capture events were found in 6 of 211 blue sharks, Prionace glauca (L.), landed in the summers of 1999 and 2000 by recreational fishermen off Long Island (New York, USA). The hooks were embedded within the distal oesophagus ( n =3), or perforated the gastric wall ( n =3) and lacerated the liver ( n =2). The hooks were surrounded by excessive fibronecrotic tissue which ablated the normal anatomical structures and in the three sharks with oesophageal hooks caused partial luminal obstruction. Accompanying lesions included oesophagitis, gastritis, hepatitis and proliferative peritonitis. Aeromonas sp. and Vibrio sp. were isolated from the peritoneal fluid of one shark with peritonitis and intralesional bacteria were seen on histological examination in all sharks. This is the first report of the prevalence and pathology of retained fishing hooks in a large number of wild-caught sharks.     

The effectiveness of Shark-Management-Alert-in-Real-Time (SMART) drumlines as a tool for catching white sharks,Carcharodon carcharias,off coastal New South Wales,Australia

White (Carcharodon carcharias L.), bull (Carcharhinus leucas, Müller & Henle) and tiger (Galeocerdo cuvier, Péron & Lesueur) sharks are the primary species responsible for unprovoked shark bites. Historically, management practices were based on culling “target” shark species (i.e. white, bull and tiger sharks), which resulted in high levels of bycatch and mortality. Shark-Management-Alert-in-Real-Time (SMART) drumlines were trialled in New South Wales, Australia, aiming to optimise the capture of target shark species while minimising bycatch and mortality. Target shark species accounted for 70% of the total catch, with white sharks contributing 298 of the 350 sharks that were caught. Four animals died, and bycatch consisted of 13 species including two threatened species. Generalised linear mixed models (GLMMs) revealed a significant spatial, temporal, environmental and gear influence on white shark catch rates. SMART drumlines are a useful tool for catching target shark species with low bycatch and mortality relative to historical bather protection methods.     

Comparative Studies of the Proteolytic Activity of Crude Extracts from the Digestive Tract of Three Shark Species

Abstract

The level of pepsin, trypsin, chymotrypsin and leucine aminopeptidase (LAP) was measured in the digestive organs of Portuguese dogfish, leafscale gulper shark, and lowfin gulper shark. The highest pepsin activity was measured in the cardiac stomach. Trypsin was not detected in leafscale gulper shark, and chymotrypsin was mainly measured in the intestine. LAP was detected in all organs and species. The temperature optima of pepsin, trypsin and chymotrypsin were between 42 and 48°C and those of LAP in the 50-56°C range. Pepsin from Portuguese dogfish was considerably activated during pre-incubation. Trypsin, chymotrypsin and LAP from lowfin gulper shark were reasonably activated when pre-incubated but that was not evident in these proteases from Portuguese dogfish and leafscale gulper shark.     

Experimental infection of lemon sharks, Negaprion brevirostris (Poey), with Vibrio species

Abstract Healthy lemon sharks, Negaprion brevirostris (Poey), were inoculated with Vibrio carchariae and V. damsela , two vibrios known to cause disease in other shark species. Vibrio damsela was not recovered from the inoculated sharks; V. carchariae infected the healthy lemon sharks, but did not produce clinically observable disease. However, histological evaluation revealed active splenic and hepatic disease with Gram-negative bacteria found in association with mononuclear cells. When the experiment was repeated with a physiologically compromised lemon shark, V. carchariae was lethal for the test animal, but V. damsela was again cleared. Vibrio carchariae was also isolated from skin lesions of a lemon shark infested with monogeneans ( Dermophthirius nigrellii ). Histological evidence indicated that this shark died of protozoan infection. Thus, lemon sharks are susceptible to infection with V. carchariae which can cause subclinical disease in otherwise healthy specimens. We suggest that D. nigrellii may act as a vector of V. carchariae and that stress plays a role in the clinical manifestation of this disease.     

The sea louse Lepeophtheirus acutus (Caligidae, Siphonostomatoida, Copepoda) as a pathogen of aquarium-held elasmobranchs

Lepeophtheirus acutus Heegaard, 1943 (Caligidae, Siphonostomatoida, Copepoda), was collected from or observed on four of six elasmobranch species held at Burgers’ Zoo (Arnhem, The Netherlands). Circumstantial evidence suggested that a zebra shark, Stegostoma fasciatum (Hermann), from the wild carried the infection into the facility, where copepods reproduced and colonized additional hosts. Copepods typically attached on and about the eyes, in the mouth and occasionally about the cloaca and on the claspers. Severe ocular lesions were associated with infections on zebra sharks, a grey reef shark, Carcharhinus amblyrhynchos (Bleeker), whitetip reef sharks, Triaenodon obesus (Rüppell), and giant shovelnose ray, Rhinobatos typus Bennett, while blacktip reef sharks, Carcharhinus melanopterus (Quoy & Gaimard), and blacktip sharks, Carcharhinus limbatus (Valenciennes), living in infested aquaria showed no sign of infection. Water treatments using trichlorfon were considered primarily responsible for the eradication of copepods from hosts and infested aquaria. This case is the first report of a copepod infection being closely associated with disease and death of an aquarium‐held elasmobranch. Given its ability to infect a wide variety of elasmobranchs and promote life‐threatening lesions on some hosts, L. acutus should be considered a dangerous pathogen of captive elasmobranchs.     

A coccolithophorid algal dermatitis of the spiny dogfish, Squalus acanthias L.

Abstract. Skin diseases of sharks and algal diseases of animals are reviewed. A specific progressive skin disease of wild, laboratory-maintained and display-aquaria populations of spiny dogfish, Squalus acanthias L., observed during a 2.5-year period at Woods Hole, Massachusetts, is described. Skin lesions, from 1mm to over 1cm in diameter, developed in the following sequence: petechial and ecchymotic haemorrhages; dome-shaped vesicles; larger lesions with central ulceration; and hyperpigmented granulations in the final repair stage. A coccolithophorid algal agent could be demonstrated in skin lesions and is described. Since both sharks and coccolithophorid algae are primitive organisms, the possible evolutionary implications of algal symbionts modified to become pathogens are discussed.     

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.     

Identification and evaluation of shark bycatch in Georgia’s commercial shrimp trawl fishery with implications for management

Abstract Many US states have recreational and commercial fisheries that occur in nursery areas occupied by subadult sharks and can potentially affect their survival. Georgia is one of few US states without a directed commercial shark fishery, but the state has a large, nearshore penaeid shrimp trawl fishery in which small sharks occur as bycatch. During our 1995–1998 investigation of bycatch in fishery‐dependent sampling events, 34% of 127 trawls contained sharks. This bycatch totalled 217 individuals from six species, with Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson), the most common and finetooth shark, Carcharhinus isodon (Müller & Henle) and spinner shark, Carcharhinus brevipinna (Müller & Henle), the least common. The highest catch rates for sharks occurred during June and July and coincided with the peak months of the pupping season for many species. Trawl tow speed and tow time did not significantly influence catch rates for shark species. Gear configurations [net type, turtle excluder device (TED), bycatch reduction device] affected catch rates for shark species. Results of this study indicate gear restrictions, a delayed season opening, or reduced bar spacing on TEDs may reduce shark bycatch in this fishery.     

热带大西洋金枪鱼延绳钓兼捕鲨鱼种类组成和渔获率及其与表温的关系

根据2007年12月~2008年3月采集的热带大西洋(05°37′~12°01′N、29°00′~36°51′W)金枪鱼延绳钓渔获物数据,分析了金枪鱼延绳钓兼捕鲨鱼的种类组成、渔获量、渔获率及其与表温的关系。本次调查共捕获鲨鱼8种,隶属3目7科7属,总渔获尾数为633 ind,总渔获量达26 837.4 kg,其中大青鲨为主要兼捕种类。各种鲨鱼渔获率平均值在0.003~1.524 ind/1 000 hooks之间,其中大青鲨最高,其值为1.524 ind/1 000 hooks,大眼砂锥齿鲨最低,其值为0.003 ind/1 000 hooks。各种鲨鱼渔获率月变化不明显(ANOVA,P=0.901)。鲨鱼总渔获率和大青鲨渔获率与表温都呈显著性负相关。大青鲨主要出现渔场的表温范围为24.6~25.8℃。     

Distribution,body length,and abundance of blue shark and shortfin mako offshore of northeastern Japan,as determined from observed pelagic longline data, 2000–2014

Longline surveys have been conducted in the Northwest Pacific Ocean from 2000 to 2014 using chartered commercial longline vessels. Each year, two cruises were conducted offshore of northeastern Japan from mid‐April to mid‐June. For each longline set during the surveys, onboard scientists collected detailed biological information about the species caught, such as the size and sex, and recorded the catch numbers for all species. Blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) have eurythermal distributions, but the application of a generalized additive model (GAM) showed that the sea surface temperatures (SSTs) at catch sites positive for shortfin mako were warmer than those for blue shark. On the basis of the GAM, the probabilities of occurrence of both sharks differed by size category: small sharks had a narrower SST range than that of large sharks. Most catches of both sharks were juveniles, and the nominal catch rate of blue shark was more than 10 times that of shortfin mako. The standardized catch per unit effort (CPUE) for both species was calculated using a generalized linear model (GLM) with negative binomial errors, or a delta‐lognormal GLM. The standardized CPUE for blue shark in the second quarter of the year peaked in the mid‐2000s and then decreased, but it has been increasing since 2012. The CPUE for shortfin mako in the second quarter generally increased, with fluctuations.     

Capture time,size and hooking mortality of bottom longline-caught sharks

The primary gear type used to harvest coastal sharks in the U.S. Atlantic shark fishery is bottom longline. Recent stock assessments have found several species of coastal sharks in U.S. Atlantic Ocean waters have declined from 60% to 80% of virgin levels. To aid in stock rebuilding, alternative gear restriction measures such as reduced soak time, restrictions on the length of gear, and fishing depth restrictions have been considered but not implemented. In order to evaluate the effectiveness of some of these management measures, controlled experiments were performed using hook timers and time depth recorders, assessing the factors affecting mortality during longline capture for the four most abundant species that incurred at-vessel mortality: sandbar (Carcharhinus plumbeus), blacktip (Carcharhinus limbatus), bull (Carcharhinus leucas), and blacknose (Carcharhinus acronotus). Our results indicate that as hook time and shark size increased mortality rates for the sandbar and blacktip sharks increased. Predicted models indicated mortality rates increased steadily for the three species but appeared to increase the most after 10, 6, and 1 h on the hook for sandbar, blacktip and blacknose shark, respectively. Sandbar sharks larger than approximately 170 cm FL are more susceptible to hooking mortality. Blacknose shark mortality rates increased as hook time increased but bull shark mortality rates were not affected by any factor. The probability of a hook being bitten increased the most between 5 and 12 h after the fishing gear had been set and the mean amount of time hooks were in the water prior to being bitten was 4, 5 and 9 h for sandbar and blacknose sharks, blacktip, and bull sharks, respectively. A significant difference was found between these means for sandbar and bull sharks and between blacknose and bull sharks. Shark species were commonly caught at different temperature and depth ranges. These results could be used by fisheries management to implement restrictions of fishing depth and soak time to aid in the recovery of coastal sharks species.     

Effects of temperature on power output and contraction kinetics in the locomotor muscle of the regionally endothermic common thresher shark (Alopias vulpinus)

The common thresher shark (Alopias vulpinus) is a pelagic species with medially positioned red aerobic swimming musculature (RM) and regional RM endothermy. This study tested whether the contractile characteristics of the RM are functionally similar along the length of the body and assessed how the contractile properties of the common thresher shark compare with those of other sharks. Contractile properties of the RM were examined at 8, 16 and 24?°C from anterior and posterior axial positions (0.4 and 0.6 fork length, respectively) using the work loop technique. Experiments were performed to determine whether the contractile properties of the RM are similar along the body of the common thresher shark and to document the effects of temperature on muscle power. Axial differences in contractile properties of RM were found to be small or absent. Isometric twitch kinetics of RM were ~fivefold slower than those of white muscle, with RM twitch durations of about 1?s at 24?°C and exceeding 5?s at 8?°C, a Q(10) of nearly 2.5. Power increased approximately tenfold with the 16?°C increase in temperature, while the cycle frequency for maximal power only increased from about 0.5-1.0?Hz over this temperature range. These data support the hypothesis that the RM is functionally similar along the body of the common thresher shark and corroborate previous findings from shark species both with and without medial RM. While twitch kinetics suggest the endothermic RM is not unusually temperature sensitive, measures of power suggest that the RM is not well suited to function at cool temperatures. The cycle frequency at which power is maximized appeared relatively insensitive to temperature in RM, which may reflect the relatively cooler temperature of the thresher RM compared to that observed in lamnid sharks as well as the relatively slow RM phenotype in these large fish.     

Catching sharks: recreational saltwater angler behaviours and attitudes regarding shark encounters and conservation

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Temperature effects on the blood oxygen affinity in sharks

In fish, regional endothermy (i.e., the capacity to significantly elevate tissue temperatures above ambient via vascular heat exchangers) in the red swimming muscles (RM) has evolved only in a few marine groups (e.g., sharks: Lamnidae, Alopiidae, and teleosts Scombridae). Within these taxa, several species have also been shown to share similar physiological adaptations to enhance oxygen delivery to the working tissues. Although the hemoglobin (Hb) of most fish has a decreased affinity for oxygen with an increase in temperature, some regionally endothermic teleosts (e.g., tunas) have evolved Hbs that have a very low or even an increased affinity for oxygen with an increase in temperature. For sharks, however, blood oxygen affinities remain largely unknown. We examined the effects of temperature on the blood oxygen affinity in two pelagic species (the regionally endothermic shortfin mako shark and the ectothermic blue shark) at 15, 20, and 25 °C, and two coastal ectothermic species (the leopard shark and brown smooth-hound shark) at 10, 15, and 20 °C. Relative to the effects of temperature on the blood oxygen affinity of ectothermic sharks (e.g., blue shark), shortfin mako shark blood was less affected by an increase in temperature, a scenario similar to that documented in some of the tunas. In the shortfin mako shark, this may act to prevent premature oxygen dissociation from Hb as the blood is warmed during its passage through vascular heat exchangers. Even though the shortfin mako shark and blue shark occupy a similar niche, the effects of temperature on blood oxygen affinity in the latter more closely resembled that of the blood in the two coastal shark species examined in this study. The only exception was a small, reverse temperature effect (an increase in blood oxygen affinity with temperature) observed during the warming of the leopard shark blood under simulated arterial conditions, a finding that is likely related to the estuarine ecology of this species. Taken together, we found species-specific differences in how temperature affects blood oxygen affinity in sharks, with some similarities between the regionally endothermic sharks and several regionally endothermic teleost fishes.     

A viral dermatitis of the smooth dogfish, Mustelus canis (Mitchill)

Abstract. A viral infection of the smooth dogfish, Mustelus canis (Mitchill), a squaliform shark, is described. The disease was found and observed in wild, laboratory-maintained and aquaria-displayed populations of smooth dogfish of the Woods Hole area of Massachusetts during a 2.5-year period. The disease was characterized by the progressive development of gross and microscopic herpes-like skin lesions. Electron microscopic examination revealed cellular pathology, viral replication and transport, and virions that conformed to those of herpesvirus infection. This study is the first report of a viral infection in elasmobranchs. The comparative pathology and implication for wild and captive shark populations is discussed.     

Standardized catch and survival rates,and effect of a ban on shark retention,Palau pelagic longline fishery

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