The fish community structure in Tjeukemeer in relation to fishery and habitat utilization

The fish community in Tjeukemeer was monitored from 1971 to 1988 by trawling, and during the summer of 1988 the distribution of the more abundant species was determined in relation to size and location. Bream, pikeperch and smelt were the most dominant fishes, whereas roach, white bream, perch and ruffe comprised <10% of the total catches. After the termination in 1977 of the intensive gillnet fishery both pikeperch >50 cm and bream >30 cm increased in biomass, but roach >15 cm and perch >15 cm virtually disappeared and pikeperch <50 cm substantially decreased. Only smelt, ruffe, white bream and bream <30 cm hardly changed in biomass. Bream, pikeperch, perch and smelt were restricted to the open water zone, but roach <15 cm and 0 + bream were confined to the littoral zone. White bream and ruffe did not show a distinct habitat preference. Because the recruitment of smelt is largely dependent on immigration from the IJsselmeer, a feed-back between the smelt and pikeperch population is lacking. Because the carrying capacity of the pikeperch population is mainly determined by smelt, the other fish <15 cm are very vulnerable to predation when the smelt population is consumed, before a new year-class of smelt is recruited, or when the smelt fails to recruit. The vulnerability to predation of the different species and their feeding habits are discussed in relation to their distribution.     

Simulation of the entanglement of a North Atlantic right whale (Eubalaena glacialis) with fixed fishing gear

Population estimates of the critically endangered North Atlantic right whale (Eubalaena glacialis) put the number of individuals at 458 with the actual number likely being lower due to a recent unusual mortality event. Entanglement with fixed fishing gear is the most significant cause of mortality of North Atlantic right whales. There remains little documentation of how North Atlantic right whales become enwrapped during an encounter with fixed fishing gear. In order to gain a better understanding of how entanglements might occur, an interactive simulator was developed that allows the user to swim a virtual whale model using a standard game controller through a gear field in an attempt to re‐create an entanglement. The morphologically accurate right whale model produces realistic swimming motions and is capable of pectoral fin motions in response to user input. Using the simulator, gear entanglements involving the pectoral flippers including ropes wrapping around the body and entanglements involving the tailstock were re‐created. Entanglements involving the pectoral flippers with body wraps were more easily generated than entanglements involving the tailstock only. The simulator should aid scientists, fisheries experts, fishing gear designers, and bycatch reduction scientists in understanding entanglement dynamics and testing potential new gear configurations.     

Entanglement‐scar acquisition rates and scar frequency for Bering‐Chukchi‐Beaufort Seas bowhead whales using aerial photography

The Bering‐Chukchi‐Beaufort Seas (BCBS) bowhead whale (Balaena mysticetus) has been considered at low‐risk for entanglement injuries and ship strikes because their range is mainly north of commercial fisheries; nevertheless, changes to their arctic habitat, including a longer open water period and declining sea ice, have resulted in increasing commercial activity and concern about fisheries interactions. We examined interyear matches (between 1985 and 2011) from a photo identification project and identified whales that had acquired entanglement injuries. We estimated the probability of a bowhead acquiring an entanglement injury using two statistical methods: interval censored survival analysis and a simple binomial model. Both methods give similar results, suggesting a 2.2% (95% CI: 1.1%–3.3%) annual probability of acquiring a scar. We also include an entanglement scar frequency analysis of aerial photographs from the 2011 spring and fall surveys near Point Barrow, Alaska, which suggest 12.4% of live bowheads show evidence of entanglement scarring. Entanglement rates for the BCBS bowhead stock are lower than many other large whale stocks, and abundance has increased over the past 35 yr; however, our findings indicate that fishing gear entanglement is a more serious concern for the BCBS bowhead whale population than previously thought.     

Fishing gears involved in entanglements of minke whales (Balaenoptera acutorostrata) in the East Sea of Korea

Entanglement of marine mammals in fishing gear is a global issue. It is considered a significant threat to minke whales (Balaenoptera acutorostrata) in the East Sea of Korea. A total of 214 entanglements of minke whales in this area between 2004 and 2007 were used to investigate types and parts of fishing gears involved in entanglements. The majority of entanglements were mainly caused by three types of fishing gears: set nets, pots, and gill nets (n= 207, 96.7%). Other entanglements were associated with bottom trawls, purse seines, and trawls. A total of 65 entanglements were attributed to the main and branch lines of fishing gears. The most common body part of minke whales which attached to fishing gears was the mouth (n= 63, 30.4%). Most entanglements took place within 10 nmi from land (n= 179, 86.5%), and between 10 and 220 m of water depth. The mean length of entangled minke whales in set nets was significantly smaller than that of whales in pots and gill nets samples (P < 0.001). Also, the mean body length of minke whales that entangled in the coastal area and shallow waters was significantly shorter than that of whales in the offshore area and deep waters (P < 0.001). This information can be used as fundamental data to conserve and manage this population of minke whales in the East Sea of Korea, and also to modify fishing gear to reduce entanglements. Future studies should focus on investigating the impact of these entanglements on the population and the effectiveness of mitigation measures to reduce entanglements of minke whales in this area.     

Assessing changes in numbers and distribution of large whale entanglements in Newfoundland and Labrador,Canada1

Entanglements of large whales in commercial fisheries in Newfoundland and Labrador, Canada, have been consistently recorded since 1979, as part of a program aimed at releasing captured animals and reducing costs to fishermen. This data set represented an opportunity to identify fisheries posing particular entanglement risks to local whale populations. Data were assessed over the periods 1979–1992 and 1993–2008, corresponding to distinct phases in fisheries distribution and intensity. Between 1979 and 2008, 1,209 large whale entanglements were recorded in Newfoundland and Labrador. These were mostly humpback whales (Megaptera novaeangliae; 80%) and minke whales (Balaenoptera acutorostrata; 15%). Dramatic declines in reported inshore whale entanglement rates were observed following the 1992 moratorium on Atlantic cod (Gadus morhua) fisheries. Recently, more entanglements have been reported further offshore, largely due to expansion of fisheries targeting snow crab (Chionoecetes opilio). For all whale species, entanglement rates and associated mortality rates varied considerably in different fishing gear. Fractions of humpback and minke whales found dead in different fishing gear differed substantially, with minke whales far more likely to be found dead than humpback whales.     

The role of OsCOM1 in homologous chromosome synapsis and recombination in rice meiosis

COM1/SAE2 is a highly conserved gene from yeast to higher eukaryotes. Its orthologs, known to cooperate with the MRX complex (Mre11/Rad50/Xrs2), are required for meiotic DNA double‐strand break (DSB) ends resection and specific mitotic DSB repair events. Here, the rice (Oryza sativa, 2n = 2x = 24) COM1/SAE2 homolog was identified through positional cloning, termed OsCOM1. Four independent mutants of OsCOM1 were isolated and characterized. In Oscom1 mutants, synaptonemal complex (SC) formation, homologous pairing and recombination were severely inhibited, whereas aberrant non‐homologous chromosome entanglements occurred constantly. Several key meiotic proteins, including ZEP1 and OsMER3, were not loaded normally onto chromosomes in Oscom1 mutants, whereas the localization of OsREC8, PAIR2 and PAIR3 seemed to be normal. Moreover, OsCOM1 was loaded normally onto meiotic chromosomes in Osrec8, zep1 and Osmer3 mutants, but could not be properly loaded in Osam1, pair2 and OsSPO11‐1^RNAi plants. These results provide direct evidence for the functions of OsCOM1 in promoting homologous synapsis and recombination in rice meiosis.     

Direct estimates of the selectivity of a multimesh and a series of single gillnets for brown trout

Hatchery brown trout Salmo trutta (1406) of length 5–20 cm were released into a 7.5 ha shallow lake. They were recaptured with 28 multimesh gillnets of a type proposed for use in the Nordic countries and 42 single gillnets of mesh size 8–22 mm (knot to knot). Corrected for the effect of different twine thicknesses, the single nets showed the highest selectivity for 16.5 mm and smaller meshes and the multimesh nets for the larger meshes. The height of the selectivity curves increased exponentially with mesh size, and most distinctly for the multimesh nets. Over a limited range of mesh sizes the selectivity of the two types of net did not differ much. Extended over mesh sizes 10.0–55.0 mm, the catching abilities of the two types of net became considerably different.     

The effects of food-web management on fish assemblage dynamics in a north temperate lake

There was an intensive trawl fishery in the Enonselkä basin in Lake Vesijärvi (southern Finland) in 1989–1993 and thereafter the fishing intensity declined. The fish assemblage dynamics were studied both during the years of intensive trawling and for 3 years afterwards. Roach Rutilus rutilus dominated the fish assemblage before the mass removal. The intensive trawling effectively diminished the roach stock and the present fishing intensity has been sufficient to prevent its recovery. There were significant decreasing trends in the gillnet cpue (catch per unit effort) of bream Abramis brama (L.) and bleak Alburnus alburnus (L.) while increasing trend was observed in cpue of ruffe Gymnocephalus cernuus (L.) and vendace Coregonus albula (L.). Perch Perca fluviatilis L. and pikeperch Stizostedion lucioperca (L.) showed variations in cpue but no trends existed. The proportion of cyprinids decreased while that of percids and coregonids increased in the catches. The changes in the fish assemblage were induced by the intensive fishing and by the concomitant decline in the ecosystem productivity.     

Consequences of injuries on survival and reproduction of common bottlenose dolphins (Tursiops truncatus) along the west coast of Florida

Accurate identification of human‐induced injuries that lead to death or interfere with reproduction is important for marine mammal management, as deaths exceeding established limits can lead to restrictions on fisheries or vessel operations. The fates of cetaceans last seen swimming with attached gear, particularly in pelagic fisheries, or with vessel strike lacerations, have been difficult to predict. Survival and reproduction data from long‐term research on resident common bottlenose dolphins near Sarasota, Florida were examined relative to consequences of fishing gear ingestion, line entanglements, vessel strikes, and amputations of unknown origins. Fishing hooks embedded in the throat, goosebeak, or esophagus, or line wrapped around the goosebeak, generally lead to death. Multiple, constrictive line wraps around fin insertions can lead to amputation, blood loss, impaired mobility, or infection. Dolphins with ingested gear or severe entanglements may swim away with the gear, but likely die later. Propeller injuries involving only soft tissue were often survivable. Some dolphins survived amputations of the distal ends of fins, and continued to reproduce. As a precautionary approach, dolphins with ingested gear or severe constrictive entanglements should be considered mortalities, but extrapolations of findings from coastal bottlenose dolphins to other cetaceans and different gear must be done with caution.     

Potential for bowhead whale entanglement in cod and crab pot gear in the Bering Sea

Bowhead whales (Balaena mysticetus) of the western Arctic stock winter in ice‐covered continental shelf regions of the Bering Sea, where pot fisheries for crabs (Paralithodes and Chionoecetes spp.) and Pacific cod (Gadus macrocephalus) pose a risk of entanglement. In the winter of 2008–2009 and 2009–2010 the spatial distribution of 21 satellite tagged bowhead whales partially overlapped areas in which pot fisheries for cod and blue king crab (Paralithodes platypus) occurred. However, these fisheries ended before whales entered the fishing areas, thus avoiding temporal overlap. A fishery for snow crab (Chionoecetes opilio) typically runs from January to May and provides the greatest potential for bowhead whales to encounter active pot gear. Tagged whales did not enter the area of the snow crab fishery during this study and generally remained in areas with >90% sea ice concentration, which is too concentrated for crab boats to penetrate. Pack ice sometimes overruns active fishing areas, resulting in lost gear, which is the most likely source of entanglement. The western Arctic stock of bowhead whales was increasing as of 2004; as such, incidental mortality from commercial pot fisheries is probably negligible at this time. Regardless, entanglement may increase over time and should be monitored.