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

Abstract

The Clyde Sea Nephrops ®shery produces ca. 25 000 t y 21 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±270 min duration) and sorting on deck. Brittlestars Ophiura ophiura were most vulnerable with 100% incurring damage, followed by squat lobsters Munida rugosa (57%) and star®sh 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-speci®c morphological and behavioural characteristics. Vessel type, tow duration and animal size had a major in¯uence on damage to the epibenthic invertebrates caught. While damage may potentially be repaired, survival is adversely affected and sublethal effects might signi®cantly impair ®tness of frequently trawled individuals and populations. q

Catch me in winter! Seasonal variation in air temperature severely enhances physiological stress and mortality of species subjected to sorting operations and discarded during annual fishing activities

“…This conclusion is further supported by the indication that 24 h are necessary for fully recovering the induced physiological impairment (Bergmann et al, 2001b) and that the occurrence of sublethal damages, such as limb loss, hamper the foraging efficiency and agonistic behavior of crabs (Pranovi et al, 2001;Bergmann et al, 2001a). However, data from surveys show a rather stable situation for the Northern Adriatic Sea (Raicevich, 2004).…”

“…These aspects are reflected, for example, by the pronounced imbalance in terms of damage, physiological stress, and survival among the species subjected to trawling activities. In fact during the fishing process, which includes not only capture by the fishing gear, but also the exposure on deck during commercial catch sorting operations, the individuals may suffer physical damage (Bergmann et al, 2001a;Pranovi et al, 2001) and physiological stress due to thermal shocks and exposure to air (Bergmann et al, 2001b;Gamito & Cabral, 2003) which can lead to high mortality rates (Kaiser & Spencer, 1995;Bergmann & Moore, 2001). Among the discarded species, crustaceans constitute a prominent part of the total biomass and represent an excellent candidate to assess the physical and physiological effects of trawling and sorting procedures (Bergmann et al, 2001b;Pranovi et al, 2001).…”

Discard analysis and damage to non-target species in the "rapido" trawl fishery

“…Species with external shells (e.g. bivalves, gastropods and hermit crabs) were well protected (Bergmann et al 2001) and rarely damaged by the rapido gear (Hall-Spencer et al 1999).…”

“…Another, and often complementary, approach evaluates injuries sustained by non-target species, estimated using damage scales, as proposed by Wassenberg and Hill (1989), Kaiser and Spencer (1995), Hill et al (1996), Kaiser (1996), Farmer et al (1998), and, more recently, by Prena et al (1999), Bradshaw et al (2000), Mensink (2000), Salini (2000), Bergmann and Moore (2001a, b) and Bergmann et al (2001). This approach allows an evaluation of the relative fragility of non-target species, which could be an integral part of their sensitivity (sensu MacDonald et al 1996); furthermore, a ®rst estimate (underestimated and here referred to as``minimum lethal rate'') of the mortality induced by the rapido ®sh-eries can be obtained considering animals whose bodies have been completely crushed.…”

Laboratory Study of the Impact of Repetitive Electrical and Mechanical Stimulation on Brown Shrimp Crangon crangon

“…This may result in a higher mortality of large shrimp, resulting IMPACT OF ELECTRICAL AND MECHANICAL STIMULATION ON BROWN SHRIMP in a smaller average size for the surviving individuals. Indeed, physical injuries have been shown to affect survival adversely (Bergmann et al 2001;Depestele et al 2014), which may be caused by damage to their fragile exteriors (Kaiser and Spencer 1995). Moreover, injuries demand extra expenditures of energy with subsequent decreases in growth and molt increments (Bennett 1973), which would explain the difference in the percentage of molts encountered.…”