Dependency of Japanese harbor seals (Phoca vitulina) on salmon set nets at Cape Erimo,Hokkaido, Japan

In this study, we observed the behavior of two age groups of harbor seal (Phoca vitulina richardii), i.e., yearlings, which often become bycaught and individuals 2 yr or older, during their stays at salmon set nets at Cape Erimo, Japan. From July to November 2011–2015, acoustic receivers that track tagging seals were attached to three set nets located near the haul‐out site. Our observations showed that the mean visit interval and the mean stay of seals at the set nets during fishing operations were significantly higher than before operations. A cluster analysis, where Cluster 1 consisted of seals that spent a long time at the set nets and Cluster 2 consisted of the other seals, showed that seals in Cluster 1 visited the set nets every day, while Cluster 2 seals visited once every 3–5 d. In addition, age 2 + seals in Cluster 1 stayed longer at regular time frames (at night), suggesting that individuals of this age group in Cluster 1 are highly dependent on the salmon set nets as foraging sites at night. It is especially clear that the set nets near the haul‐out site have influenced the foraging ecology of some seals.     

INTERACTIONS BETWEEN SOUTH AFRICAN FUR SEALS and THE PURSE-SEINE FISHERY

Operational interactions occur between South African (Cape) fur seals and the purse-seine fishery in South Africa. Seals eat fish from the nets but the main concern is the activity of seals causing fish to sound, resulting in loss, or partial loss of the catch. Detectable loss occurs on approximately 5% of hauls. In addition to this, smaller quantities may be lost on each haul as seals depress the net float line while moving into and out of the net. The cost of seal interference is difficult to quantify because the mass of fish lost is not known, and the loss is essentially one of additional fishing time required to fill the total allowable catch for the fishery. An estimate of the cost is calculated as between 1.6% and 4.1% of the landed value of the fishery. Some seals are killed by fishermen when they pose a potential threat to the safety of the crew aboard, and some may drown if caught in the net or pump. Overall this is probably fewer than a thousand seals per year. It is also known that if seals are thought to be disturbing the fish, these seals near the nets may be deliberately killed by purse-seine fishermen. Overall this mortality, whether deliberate or incidental, is probably negligible in terms of the population size of South African fur seals.     

Host characteristics and infection level of an intestinal parasite Corynosoma strumosum (Acanthocephala) in the Kuril harbor seal of Erimo Cape,Hokkaido, Japan

The Kuril harbor seal around Hokkaido is presently recovering from a resource crisis while conflicts with local fisheries have become a concern. However, its feeding habits, which are fundamental information for taking proper preventive measures, are still poorly understood. We thus examined the infection status of a trophically-transmitted parasite, Corynosoma strumosum in the seals of Erimo Cape, to assess the host's feeding habits with a practical view of the parasite as a biological indicator. A total of 2802 worms were found from 20 male and 20 female by-caught animals in salmon set nets within local fisheries during August to November 2014. The parasite abundance was explained mainly by the host's developmental stage and intestinal length while weakly affected by gender and body size, through an estimation of generalized linear models combined with hierarchical partitioning. Considering the past records that demersal fishes are the probable main sources of infection, the infection level may owe to individual host differences regarding these sources and/or feeding grounds with relating the host characteristics. This supports that the resource management of Kuril harbor seals requires careful consideration of the individual differences in feeding behavior.     

A Novel Tool to Mitigate By-Catch Mortality of Baltic Seals in Coastal Fyke Net Fishery

Developing methods to reduce the incidental catch of non-target species is important, as by-catch mortality poses threats especially to large aquatic predators. We examined the effectiveness of a novel device, a “seal sock”, in mitigating the by-catch mortality of seals in coastal fyke net fisheries in the Baltic Sea. The seal sock developed and tested in this study was a cylindrical net attached to the fyke net, allowing the seals access to the surface to breathe while trapped inside fishing gear. The number of dead and live seals caught in fyke nets without a seal sock (years 2008–2010) and with a sock (years 2011–2013) was recorded. The seals caught in fyke nets were mainly juveniles. Of ringed seals (Phoca hispida botnica) both sexes were equally represented, while of grey seals (Halichoerus grypus) the ratio was biased (71%) towards males. All the by-caught seals were dead in the fyke nets without a seal sock, whereas 70% of ringed seals and 11% of grey seals survived when the seal sock was used. The seal sock proved to be effective in reducing the by-catch mortality of ringed seals, but did not perform as well with grey seals.     

River flow, Atlantic salmon (Salmo salar L.) movement and rod catch in the Aberdeenshire Dee

The relationship between river flow and rod and net catches of salmon and grilse have been analysed for four of the major fisheries on the Aberdeenshire Dee. On the lower two fisheries there is a good correlation between the rod catch and the average flow on the day of the catch and the preceding 3 days but there is no such correlation at the highest fishery. There is also a good correlation between the annual flow during the rod season and the total annual rod catch at the lowest fishery, while there is an inverse correlation between the flow during the rod season and the net catch. When the nets are off there is no longer any correlation between river flow and rod catch at the lowest fishery.     

Seals and fyke nets: An investigation of the problem and its possible solution

During the last few decades, the economically important eel (Anguilla anguilla) fishery with fyke nets along the Swedish west coast has been subjected to damage caused by harbour seals (Phoca vitulina). To protect fyke nets from seals, the netting in the fish bags was replaced with stronger material. The level of damage decreased when fishing with modified fyke nets, compared with when traditional fyke nets were used. The stronger fyke nets were, however, still exposed to a notable level of attack from seals, even if the resulting damage was minor compared with that suffered by the standard fyke nets. There was no difference in the catch per unit effort when comparing the most effective modified fyke nets with the standard fyke nets. By testing exclusively modified fyke nets in certain areas, and only standard fyke nets in other fishing areas some distance away, the levels of damage were reduced in the areas with only modified fyke nets. By replacing traditional fyke nets with modified fyke nets, fishermen can make it less profitable for seals to use fyke nets as food stores, with less gear damage and zero catch losses as a result. Using modified fyke nets in the commercial eel fishery is both practical and rewarding for the fishermen.     

Trap efficiency for Glossina pallidipes (Diptera: Glossinidae) at Nguruman, south-west Kenya

An incomplete ring of electric nets was evaluated as a means of estimating trap efficiency for Glossina spp. This methodology assumes flies approach the trap directly, and then enter, or leave directly in random directions. These results showed that the ratio of the number of flies intercepted on the outside of the electric nets to the number on the inside was lower than predicted by this single-approach behavioural model. Moreover, an incomplete ring of nets around a trap reduced trap catch more than the model predicted. These inconsistencies were greater early in the day, and greater for females than for males. It is suggested that flies may make several approaches to a trap before entering or departing. This mixes arriving and departing flies on each side of the electric nets. Use of a complete ring of nets around a trap to estimate trap efficiency entails fewer behavioural assumptions. Catches at a complete ring around a trap were compared to catches in a trap without nets, replicated in a cross-over design. The efficiency of an odour baited NG2G trap was estimated to be 58% for males and 37% for females. Biconical traps were much less efficient. Both trap types were less efficient in the early morning, suggesting entry response is temperature dependent. The NG2G trap was more efficient for non-teneral nulliparous females than for other ages. For both trap types there was little difference between mean fat content of approaching and trapped males, but the mean fat content of trapped females was lower than that of approaching females.     

The effect of weather on the concentration of pollen within sugar-beet seed crops

The concentration of pollen in the air within diploid open-pollinated sugar-beet seed crops at Broom's Barn Experimental Station increased between 05.00 and 09.00 G.M.T. as relative humidity became less than 90%, was greatest between 09.00 and 11.00, when relative humidity was c. 75%, and gradually decreased towards evening. The average pollen concentration during 24 h periods ranged from 170 to 12400/m³ being greatest on fine, windy, dry days after periods of cooler weather. Rain during the morning washed pollen out of the air and damaged developing anthers, but rain in the late afternoon following a sunny morning seemed hardly to affect the pollen catch, while rain at night sometimes caused an immediate temporary increase in pollen concentration. Most pollen was released between 27 June and 31 July in all years (1965-7); more in the first than in the second half of July. 1965 was cool and damp, 1967 warm and dry, 1966 warm and dry early, and cool and wet late. The total pollen catch in 1965 was 83% and in 1966 31% of that in 1967 but the percentage germination of seed harvested in the 3 years was similar. The total pollen catch on a trap 230 m east of the 1965 crop was c. 1% of the catch within the crop on days with gusty westerly winds and the catch on a trap c. 46 cm above the 1966 crop averaged 78.6% of that at the level of most flowers.     

The biology of pygmy whitefish, Prosopium coulterii, in a closed sub-boreal lake: spatial distribution and diel movements

Using gillnets and trap nets, we examined the spatial distribution, diel movements, and environmental tolerances of pygmy whitefish, Prosopium coulterii, in a small boreal lake in north-central British Columbia. Most gillnets were set below the thermocline but we also fished a shore net in the littoral zone. During the ice-free season (May to November) there was a strong diel onshore–offshore movement: during the day pygmy whitefish were offshore and below the thermocline (water temperatures of 4–6°C) but at night they were inshore and above the thermocline (water temperatures of 12–18°C). This onshore–offshore movement occurred close to the bottom and, regardless of where they were caught, most fish were <4 m off the bottom. Oxygen concentrations in most of the hypolimnion dropped to <5.0 mg l⁻¹ in June and by late August to <1.0 mg l⁻¹; indicating pygmy whitefish can tolerate low oxygen conditions. The catch of pygmy whitefish in gillnets set below the thermocline was highly skewed: 53% of the nets were empty, 37% caught 18 or less fish, and 10% caught 70% of the total catch (742 fish). Trap nets produced similarly skewed results: most trap net sets caught no pygmy whitefish but one set caught over 2,000 individuals. Our catch data suggest that in Dina Lake #1 some pygmy whitefish aggregate.     

Health status of harp seals (Phoca groenlandica) and hooded seals (Cystophora cristata) on Sable Island,Nova Scotia,Canada, concurrent with their expanding range

Beach surveys for harp (Phoca groenlaandica) and hooded (Cystophora cristata) seals documented a dramatic increase in their numbers on Sable Island in mid 1990s. In the 1980s, no more than five animals of both species were observed on this island each year, however, during late 1994 to 1998, 1,191 harp and 870 hooded seals, mostly young animals, were recorded. Although some of these seals had been killed by sharks, most (roughly 75%) were found alive or as intact carcasses on the beach, and some of the live seals were later found dead. Emaciation/starvation was considered the primary cause of death in seals that were not obviously killed by sharks. Factors that may have compounded this poor body condition included gastric impaction with abnormal ingesta, hemorrhagic diathesis possibly induced by parasitic migration and secondary vasculitis, and stomatitis (in hooded seals only). Some harp and hooded seals expanding their range in recent years may be unable to feed successfully, although the reasons for this are unclear.     

INCIDENTAL MORTALITY OF NORTHERN SEA LIONS IN SHELIKOF STRAIT, ALASKA

The incidental catch of northern sea lions ( Eumetopias jubatus ) in the walleye pollock ( Theragra chalcogramma ) joint-venture fishery in Shelikof Strait, Alaska, was studied during 1982–1984 to assess the nature and magnitude of the catch. Data were obtained by placing U.S. observers on foreign processing vessels. Dead sea lions recovered from trawl nets were counted, sexed and measured, teeth were removed for age determination by dental laminae; and stomach contents were analyzed. Although the fishery has continued to expand both in number of boats and estimated total catch (74,136 metric tons [t] in 1982 to 171,539 t in 1984), the estimated incidental catch of northern sea lions has declined (ranging from 958 to 1,436 in 1982, 216 to 324 in 1983 and 237 to 355 in 1984). Of the sea lions processed, 73 percent were caught between 2000 and 0500 h, probably during net retrieval. Most caught sea lions were females ranging in age from 1–25 yr with a mean age of 6.43 yr; 79 percent of the females were sexually mature and probably part of the reproducing population. Males had a mean age of 4.8 yr and only 12 percent were old enough to obtain and defend territories. Analysis of stomach contents showed that the sea lions consumed pollock the same size as that taken by the commercial fishery. The impact of the incidental catch on the Gulf of Alaska sea lion population is unknown.     

Does increased abundance of sea lice influence survival of wild Atlantic salmon post‐smolt?

A synthesis of results from two projects was assessed to analyse possible influence of sea lice Lepeophtheirus salmonis on marine Atlantic salmon Salmo salar survival. During the years 1992–2004, trawling for wild migrating post-smolts was performed in Trondheimsfjord, a fjord in which no Atlantic salmon aquaculture activity is permitted. Prevalence and intensity of sea lice infections on migrating wild post-smolts differed between years. A correlation analysis between 1 sea-winter (SW) Atlantic salmon catch statistics from the River Orkla (a Trondheimsfjord river) and sea lice infections on the migrating smolts in the Trondheimsfjord was not significant. Up to 2% reduction in adult returns due to sea-lice infection was expected. In addition, experimental releases from 1996 to 1998 with individually tagged groups of hatchery-reared Atlantic salmon smolts given protection against sea-lice infection was performed. Higher recaptures of adult Atlantic salmon from 1998 treated smolts compared to the control group may correspond to high abundance of sea lice found on the wild smolt, and may indicate influence on post-smolt mortality. These studies indicate that post-smolt mortality in Trondheimsfjord is marginally influenced by sea lice infection; however, the methods for assessing wild smolt mortality might be insufficient. Higher infections of sea lice farther out in the fjord may indicate more loss in Atlantic salmon returns in some years.     

Short-term effects of mowing on insect communities in Japanese peach orchards

A population survey of insects was conducted at peach orchards in Okayama Prefecture, western Japan, every 2 weeks during May–October in 2011. Pitfall traps were used to sample more than 4000 insects at 10 orchards: 8 orchards where ground vegetation had been managed by mowing and 2 with management by herbicide application. Numbers of insect species (species richness) and numbers of insects captured in pitfall traps (trap catches) were greater after mowing. Details of the effects of mowing on insect communities were examined at four orchards that had been mowed. Results suggest that species richness and trap catches increase up to 5 days after mowing and then return to their original state. Increased species richness and trap catches were mainly attributable to the increase of ants (Formicidae) and carabids (Carabidae). These results suggest that ants and carabids actively seek prey animals that have been killed, injured, or damaged by mowing.     

Migration of wild and hatchery reared smolts of Atlantic salmon, Salmo salar L., through lakes

In 1982 and 1983 descending wild Atlantic salmon smolts, Salmo salar L., were caught in a fish-trap at the mouth of the River Imsa. Together with hatchery-reared smolts of the River Imsa strain they were tagged and released at three different sites of the Imsa-Lutsi watercourse: in the Imsa River 1 km above the trap, and in two lakes, 3 and 11 km upstream of the trap. The recapture-rate in the fish-trap decreased with increased migration distance. The hatchery-reared smolts migrated downstream faster than wild smolts. Lake-released smolts were considerably delayed in their downstream migration compared to the river released smolts. The results are discussed in relation to environmental and physiological parameters.     

Cumulative stress-induced mortality of gizzard shad in a southeastern U.S. reservoir

Synopsis Starvation was apparently responsible for a large die-off of gizzard shad, Dorosoma cepedianum, in several east Tennessee reservoirs during the spring of 1983. Condition indices, calorific equivalents, lipids, and blood parameters of electrofished (control) shad from Watts Bar Reservoir were significantly higher than these parameters for recently dead shad and for stressed shad, indicating that the stressed and dead fish were at similar levels of physiological condition. We hypothesize that mortality due to starvation resulted from a year-long series of unusual environmental conditions beginning with an abnormally warm spring in 1982 which delayed spawning for some shad, a mild winter in 1982–1983 which increased metabolic demands, and an unusually cool spring in 1983 which delayed food availability. These events may have acted in a cumulative fashion, with each inducing additional increments of stress until lipid stores were depleted to a nonrecovery level, which appears to be about 4% of dry body weight. At least 10% of the adult gizzard shad died of starvation. Most predators were probably not adversely affected by the die-off because of the high availability of shad smaller than 16 cm (total length) and the vulnerability of stressed shad to predation.Energy Division, Oak Ridge National Laboratory     

Gargoor trap fishery in Kuwait,catch rate and species composition

Kuwait's fisheries include shrimp trawlers, gill nets, intertidal stake nets, and demersal fish traps, known locally as gargoor. The gargoor fishery used to be the nation's most important in terms of value and landings volume, but declines in catch rates have reduced its ranking. This paper describes the status of the gargoor artisanal fishery. The main landings place was sampled for catch and effort, and fish length‐frequency data from May 2003 to December 2005. The catch rate, monthly average number of boats operating, and the number of gargoor cleared were estimated for dhow boats fishing in Kuwait's waters and international waters, and speed boats operating in Kuwait waters only. Over the duration of the study period, the speedboat catch rates were higher than those of dhow boats, i.e., 3.7 kg/trap‐pull vs. 2.6 and 2.5 kg/trap‐pull for dhows fishing in Kuwait's territorial waters and international waters, respectively. The grouper, Epinephelus coicodes, was the main species captured, contributing 19.3% and 17.8% to the dhow catch in Kuwait waters and international waters, respectively. The catch rates by dhow boats declined from an average of 4.7 kg/trap‐pull in 2003 to 2.7 kg/trap‐pull in 2005 representing a 41% decrease. If this decreasing catch rate trend continues, then fishing effort should be reduced to allow stock recovery. It is recommended that the number of gargoor fished in Kuwaiti waters should be limited and that several no‐fishing zones be established to ensure the minimum spawning stock biomass and preserve biodiversity for all fisheries.     

Population structure of odd-broodline Asian pink salmon and its contrast to the even-broodline structure

Most of the variation (99%) of Asian odd-broodline pink salmon Oncorhynchus gorbuscha , based on data at 32 variable (46 total) allozyme loci from 35 populations, occurred within populations. The remaining interpopulation variation was attributable to: (1) differences between northern (the northern Sea of Okhotsk, eastern Kamchatka Peninsula and western Kamchatka Peninsula) and southern (Hokkaido Island, Kuril Islands and Sakhalin Island) populations; (2) differences between the southern areas; (3) low variation among populations within some areas. The pattern contrasted strongly with that observed for Asian even-broodline populations, which had a strong structure, possibly related to geographic and oceanographic influences. Isolation-by-distance analyses of each of the two broodlines showed a stronger relationship (x 4·8) among even- than odd-broodline populations. Allele frequency differences between even- and odd-broodlines reflected the reproductive isolation of the broodlines. However, there were no fixed frequency differences which, considered with the differing population structures, suggests that migration-drift equilibrium has not yet obtained in one or both broodlines. The structural differences also suggest it is likely that the even- and odd-broodlines are of different ages and that one is derived from the other. Allozyme data do not provide a genealogical basis for identifying the ancestral lineage.     

Evidence for competitive dominance of Pink salmon (<Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis>) over other Salmonids in the North Pacific Ocean

Relatively little is known about fish species interactions in offshore areas of the world’s oceans because adequate experimental controls are typically unavailable in such vast areas. However, pink salmon (Oncorhynchus gorbuscha) are numerous and have an alternating-year pattern of abundance that provides a natural experimental control to test for interspecific competition in the North Pacific Ocean and Bering Sea. Since a number of studies have recently examined pink salmon interactions with other salmon, we reviewed them in an effort to describe patterns of interaction over broad regions of the ocean. Research consistently indicated that pink salmon significantly altered prey abundance of other salmon species (e.g., zooplankton, squid), leading to altered diet, reduced total prey consumption and growth, delayed maturation, and reduced survival, depending on species and locale. Reduced survival was observed in chum salmon (O. keta) and Chinook salmon (O. tshawytscha) originating from Puget Sound and in Bristol Bay sockeye salmon (O. nerka). Growth of pink salmon was not measurably affected by other salmon species, but their growth was sometimes inversely related to their own abundance. In all marine studies, pink salmon affected other species through exploitation of prey resources rather than interference. Interspecific competition was observed in nearshore and offshore waters of the North Pacific Ocean and Bering Sea, and one study documented competition between species originating from different continents. Climate change had variable effects on competition. In the North Pacific Ocean, competition was observed before and after the ocean regime shift in 1977 that significantly altered abundances of many marine species, whereas a study in the Pacific Northwest reported a shift from predation- to competition-based mortality in response to the 1982/1983 El Nino. Key traits of pink salmon that influenced competition with other salmonids included great abundance, high consumption rates and rapid growth, degree of diet overlap or consumption of lower trophic level prey, and early migration timing into the ocean. The consistent pattern of findings from multiple regions of the ocean provides evidence that interspecific competition can significantly influence salmon population dynamics and that pink salmon may be the dominant competitor among salmon in marine waters.     

Scaring seals by sound

In 1974 and 1975 a series of trials were made to investigate the effectiveness of sound as a deterrent to marauding seals at salmon netting stations. A feasibility trial was followed by experimental work on a captive juvenile Common seal. A wide variety of sounds including pure tones, Killer whale calls and recorded loud noises were transmitted and responses were recorded on videotape. While one sound appeared to elicit an alarm reaction, habituation was rapid. Field trials were carried out at netting stations at the mouth of the River Tweed which frequently suffer damage from Grey seals. Although the frequencies used spanned the entire hearing range of seals, no sound was consistently effective in scaring seals from the nets. It is concluded that the prospect of an acoustic deterrent is remote.