Effects of different slipping methods on the mortality of sardine, Sardina pilchardus, after purse-seine capture off the Portuguese Southern coast (Algarve)

Abstract

The effects of two different slipping methods on the survival, physical and physiological response of sardines, Sardina pilchardus, captured in a purse-seine fishery were investigated in southern Portugal. Sardines were collected and transferred into holding tanks onboard a commercial fishing vessel after being captured, crowded and deliberately released using two slipping procedures: standard and modified. The standard slipping procedure aggregated fish at high densities and made them “roll over” the floatline, while the modified procedure aggregated the fish at moderate densities and enabled them to escape through an opening created by adding weights to the floatline. Both slipping methods were compared with minimally harmed non-slipped sardines (sardines collected from the loose pocket of the purse seine). Survival rates were monitored in captivity over 28 days using three replicates for each treatment. The estimated survival of sardines was 43.6% for the non-slipped fish, 44.7% for the modified slipping and 11.7% for the standard slipping treatments. Scale loss indicated the level of physical impact experienced, with dead fish from the non-slipped and modified slipping technique showing significantly lower scale loss than those fish from the standard slipping treatment within the same period. Of the physiological indicators of stress measured, cortisol, glucose, lactate and osmolality attained peak values during slipping and up to the first hours after introduction to captivity. This work indicates that although delayed mortality after release may be substantial, appropriately modified slipping techniques significantly enhance survival of slipped sardines.

Physiological and flesh quality consequences of pre-mortem crowding stress in Atlantic mackerel (Scomber scombrus)

“…Behavioural activity at this stage is characterised by sustained and intense escape behaviour from the fish. Accordingly, crowding has been shown to initiate physiological responses in pelagic schooling fish that are of sufficient severity to cause mortality [16][17][18][19]. Considering that current practice involves pumping catches directly into refrigerated seawater (RSW) tanks, there is likely little opportunity for homeostatic recovery prior to death.…”

An Adapted Slipping Process to Exclude Jellyfish in the Sea of Marmara Purse Seine Fishery

“…Sharks were seen alive during the slipping process. Although this process thought to be useful for the survival of the larger vulnerable species, the complete pulling up and ultimately slipping over the headline causes more physical injury and reduces the probability of survival of slipped small size pelagic fish (Marçalo et al, 2018). Since survival of the jellyfish and little amount of anchovy after excluded from buntend of the purse seine net is not known, this issue should be examined by scientific methods.…”

“…Survival ratio of slipped species can be affected by different factors such as holding time and catch density in the bunt, size of the fish and condition factor, scale loss and water temperature (Marçalo et al, 2018). In the bunt, the catch can become highly crowded, and can be fatally harmed by oxygen depletion, exhaustion and physical injury from contact with the net and catch (Tenningen et al, 2012).…”

“…In these processes, entire or part of the catch is released by rolling the fish over the headline (floating line) of the net after partially hauling or drying-up the net. However, a modified slipping procedure is developed by Marçalo et al (2018) enable the fish to escape through an opening (escape window) created by adding weights to the float line. In this procedure, the net was bunted (manually hauled) and 4±5 sets of 10 kg weights were put along the headline to form an escape opening.…”

A haplotype-resolved draft genome of the European sardine (Sardina pilchardus)

“…Sardines were caught during commercial fishing operations in the coastal waters off Olhão, Portugal, and maintained live at the experimental fish culture facilities (EPPO) of the Portuguese Institute for the Sea and Atmosphere (IPMA), Olhão, Portugal [14]. A single adult female was anesthetised with 2-phenoxyethanol (1:250 v/v), blood was collected in a heparinized syringe, and the fish euthanized by cervical section.…”