Evaluation of open- and closed-eyed entrances on retention and escape of invasive swimming crabs and associated fauna from pots in their native range

Fishing trials targeting several invasive swimming crab species in their native habitat were undertaken using two types of collapsible pot, one with open-eyed entrances and the other with closed-eyed entrances, to analyse differences in catch retention between them. The open-eyed pot was dome-shaped with two funnel entrances located at opposite ends, whereas the closed-eyed pot had two soft sleeves that ended in slits and had to be pushed through by organisms to ingress, supposedly reducing escape. Retention fishing trials (100 pot hauls per pot type) using a 1-day soaking and fish bait confirmed no significant difference in crab catches between pot types; differences were only detected for large fish (morays and congers). A second set of 4-day escape trials (20 pots per type) was undertaken to investigate how long organisms would be detained in the pots. Escape was significantly affected, and half-residences were typically delayed by 1–2 days for most crabs and fish in closed-eyed entrance pots because the entrances closed. Closed-eyed entrances hampered escape and may be useful when longer soakings are needed; however, because no differences were detected in crab numbers between the two entrance types for short soakings, we recommend open-eyed entrance pots in order to mitigate possible ghost fishing effects from lost gear

Relative trap efficiency for recreationally caught eastern Australian blue swimmer crab (Portunus pelagicus) and associated injury and mortality of discards

Australian recreational fishers targeting Portunus pelagicus are regulated by unverified gear restrictions which, combined with size, sex and quota regulations, result in \u3e40% of their catches being discarded; all with unknown fate. To address these issues, we investigated the relative efficiency and temporal selectivity of “round”, “rectangular” and “wire” pots, and “hoop nets” set for 3, 6, and 24 h and the subsequent injury, physiological stress and mortality (in cages with controls over three days) of discarded P. pelagicus (37–85 mm carapace length – CL). Undersized (CL) and ovigerous P. pelagicus comprised 22% and 4% of the total catch. Irrespective of soak time, round pots caught significantly more P. pelagicus and teleost bycatch. Five percent of individuals lost 1–3 appendages, usually during disentanglement, and only 1.1% of discarded P. pelagicus died (all within 24 h). Haemolymph parameters were mostly affected by biological, rather than technical factors. The results support the mandatory discarding of P. pelagicus, but pot selectivity might be improved via escape vents or larger mesh sizes

Giant mud crab (Scylla serrata): relative efficiencies of common baited traps and impacts on discards

This study was initiated in response to a scarcity of data on the efficiency, selectivity and discard mortality of baited traps to target Scylla serrata. Five replicates of four traps, including “hoop nets”, rigid “wire pots”, and collapsible “round” and “rectangular” pots were deployed for 3, 6 and 24 h in two Australian estuaries. Trapped S. serrata were “discarded” into cages and monitored with controls over 3 d. All S. serrata were assessed for damage, while subsets of immediately caught and monitored individuals had haemolymph constituents quantified as stress indices. All traps retained similar-sized (8.1–19.1 cm carapace width) S. serrata, with catches positively correlated to deployment duration. Round pots were the most efficient for S. serrata and fish—mostly Acanthopagrus australis (3% mortality). Hoop nets were the least efficient and were often damaged. No S. serrata died, but 18% were wounded (biased towards hoop nets), typically involving a missing swimmeret. Physiological responses were mild and mostly affected by biological factors. The results validate discarding unwanted S. serrata for controlling exploitation, but larger mesh sizes or escape vents in pots and restrictions on hoop nets would minimise unnecessary catches, pollution and ghost fishing