P. G. Moore

Damage sustained by epibenthic invertebrates discarded in the Nephrops fishery of the Clyde Sea area, Scotland

The Clyde Sea Nephrops fishery produces ca. 25,000ty1 discards with invertebrates accounting for up to 90% of the number of animals discarded. Trawling and handling of the (by-)catch often results in physical injury, the extent of which was previously unknown.Damage sustained by invertebrate discards was assessed following commercial trawling (of 62-270min duration) and sorting on deck. Brittlestars Ophiura ophiura were most vulnerable with 100% incurring damage, followed by squat lobsters Munida rugosa (57%) and starfish Astropecten irregularis (56%). Harder-shelled species such as hermit crabs Pagurus bernhardus and queen scallops Aequipecten opercularis sustained fewer injuries (14 and 2%, respectively). Shell chipping, loss and damage of limbs were the most frequent types of injury incurred. The severity and frequency of damage was mainly correlated with species-specific morphological and behavioural characteristics. Vessel type, tow duration and animal size had a major influence on damage to the epibenthic invertebrates caught. While damage may potentially be repaired, survival is adversely affected and sublethal effects might significantly impair fitness of frequently trawled individuals and populations.

Discard composition of the Nephrops fishery in the Clyde Sea area, Scotland

Abstract Demersal fishing gear such as otter-trawls generate large amounts of unwanted by-catch. The Norway lobster ( Nephrops norvegicus ) is the most important shellfish resource in UK waters and although the fishing effort has increased considerably over past decades the ecosystem effects of this fishery have yet to be evaluated. This study provides the first assessment of the catch and discard composition from Nephrops trawls in the Clyde Sea area with particular emphasis on invertebrate discards. Nephrops constituted only between 14 and 23% of the total catch (volume); other invertebrates and fish accounted for the remainder of the catch. On an average, 9xa0kg of discards were produced per kilogram of Nephrops . The catch composition differed markedly between samples from the north and south Clyde Sea areas. Trawls from the south yielded a significantly higher biomass of Nephrops (30% cf. 4% in the north) and fish discards (55% cf. 36% in the north) whereas catches from the north contained more invertebrates (60% cf. 15% in the south). Crustaceans and echinoderms accounted for up to 83 and 73% of the discards, respectively. Samples from the north also contained a greater variety of invertebrate species (93 taxa cf. 51 taxa in the south). The differences between the two study areas are likely to be a reflection of differing bathymetries, hydrographic conditions and ground types in each area.

Seals and fisheries in the Clyde Sea area (Scotland): traditional knowledge informs science

Abstract Results obtained from circulating a questionnaire on seal/fisheries interaction around two groups of stakeholders (trawlermen and creel fishers) from the Scottish Clyde fishing fleet are presented. An overall return rate of 30% was achieved representing 664 man-years of traditional knowledge. Nowadays, most commercial fishing in the Clyde Sea area targets Norway lobsters (Nephrops norvegicus), using either towed (nephrops trawl) or static (baited creel) gear. Nephrops trawling generates a whitefish by-catch. All those respondents fishing within the confines of the Clyde Sea area reported experiencing seals interfering with their fishing activities. Both grey seals (Halichoerus grypus) and common, or harbour, seals (Phoca vitulina) occur locally but most respondents did not distinguish between them. The majority of trawlermen reported seals taking fishes from nets and damaging fishes. Only 9% of trawlermen, however, noted gear damage in spite of 91% reporting capturing seals (occasionally or rarely) in their gear. Seals caught in trawls were mostly retrieved dead (exact incidence unknown). Sixty-three percent of creelers who responded reported both damage to fishes and interference with creels. Seals may break into, or smash, creels to steal the bait and in so doing liberate catches. Contact with seals was not thought to taint fishing gear. Seals seemed to target cod (Gadus morhua) and hake (Merluccius merluccius) in trawls and seemed to select the larger individuals. Creel fishers highlighted damage to the bellies of fishes whilst trawlermen stressed damage to the tails. As much as 10% of the whitefish caught by trawlermen was unsaleable due to seal damage. Damage caused by seals was readily distinguishable from damage caused by other agents. ‘Rogue’ individual seals were not solely to blame. Typically, 9–12 seals (even sometimes as many as 25) might be encountered by any one fisher, especially when gear was being hauled. Half the trawlermen who participated regarded seals as being either a ‘considerable’ or ‘moderate’ threat to their livelihoods but 45% regarded them as a ‘minor’ or ‘non’-problem. Grey seal populations have undoubtedly increased considerably locally over the last 40 years. Eighty-six percent of trawlermen were in favour of some sort of seal cull (cf. 14% against), with some 45% of trawlermen in favour of halving seal numbers locally. Over 60% of creelers who responded were looking for even more stringent cut-backs in seal numbers, i.e. of more than 70%.

The impact of hydraulic blade dredging on a benthic megafaunal community in the Clyde Sea area, Scotland.

Abstract A study was made of the impacts on a benthic megafaunal community of a hydraulic blade dredge fishing for razor clams Ensis spp. within the Clyde Sea area. Damage caused to the target species and the discard collected by the dredge as well as the fauna dislodged by the dredge but left exposed at the surface of the seabed was quantified. The dredge contents and the dislodged fauna were dominated by the burrowing heart urchin Echinocardium cordatum, approximately 60–70% of which survived the fishing process intact. The next most dominant species, the target razor clam species Ensis siliqua and E. arcuatus as well as the common otter shell Lutraria lutraria, did not survive the fishing process as well as E. cordatum, with between 20 and 100% of individuals suffering severe damage in any one dredge haul. Additional experiments were conducted to quantify the reburial capacity of dredged fauna that was returned to the seabed as discard. Approximately 85% of razor clams retained the ability to rapidly rebury into both undredged and dredged sand, as did the majority of those heart urchins Echinocardium cordatum which did not suffer aerial exposure. Individual E. cordatum which were brought to surface in the dredge collecting cage were unable to successfully rebury within three hours of being returned to the seabed. These data were combined to produce a model of the fate of the burrowing megafauna dredged and dislodged in order to collect 10 kg of marketable razor clams.

Foraging by marine scavengers: Effects of relatedness, bait damage and hunger

Abstract Field studies using fish-baited creels have confirmed that Carcinus maenas, Necora puber and Pagurus bernhardus (Crustacea: Decapoda), Buccinum undatum (Gastropoda) and Asterias rubens (Echinodermata) are prominent scavenging species in shallow waters in the Clyde Sea area. Capture rates of these species by creels baited with dead fish plus variously damaged C. maenas were examined in the field. The addition of substantially fractured C. maenas significantly reduced the capture of conspecifics, but significantly enhanced the capture of the taxonomically unrelated species A. rubens . The remaining crustacean taxa (of the above) were unaffected by this treatment. The magnitude of th response was related strongly to the extent to which C. maenas were damaged. The effects of hunger on these responses were tested in a laboratory experiment in which the responses of starved and fed batches of C. maenas were investigated. Starved crabs remained attracted to fish bait, despite the proximity of dead conspecifics. Conversely, crabs of the fed batch were significantly more reluctant to enter creels containing damaged conspecifics. The localized presence of odours emanating from dead conspecifics did not cause crabs to remain inactive in shelter. We conclude that taxonomic relatedness to bait, degree of carcass damage and hunger of the scavenger all interact in determining foraging decision-making even by so-called generalist scavengers.