No abstract

Favaro, B., Duff, S. D., and Côté, I. M. 2013. A trap with a twist: evaluating a bycatch reduction device to prevent rockfish capture in crustacean traps. – ICES Journal of Marine Science, 70:114–122. Bycatch, or the incidental capture of non-target species, occurs in fisheries around the world, with often detrimental ecological consequences. Bycatch reduction devices (BRDs) that increase catch specificity have been used successfully in some fisheries, and the development of such devices remains an important component of the global effort to reduce bycatch rates. We tested novel devices designed to exclude juvenile rockfish (Sebastes spp.) from traps used to catch spot prawns (Pandalus platyceros), a commercially important species in British Columbia, Canada. The devices included reductions in trap opening sizes and novel bent-tunnel openings. Reducing trap opening size did not affect bycatch rates of rockfish or other non-target fish species. In contrast, bent-tunnel BRDs eliminated rockfish bycatch, and two of the bent-tunnel variants also excluded other fish species. However, prawn catch rates were reduced in all modified gear, and large prawns were often excluded more than small prawns. Videos recorded in situ revealed that prawn attempts to enter traps took longer and were more likely to fail in BRD-equipped than in unmodified traps. We conclude that bent-tunnel BRDs have the potential to be useful, but improvements are needed to increase prawn catch to levels similar to that of unmodified traps.

Summary1. Behavioural research in deep water (>40 m depth) has traditionally been expensive and logistically challenging, particularly because the light and sound produced by underwater vehicles make them unsuitably disruptive. Yet, understanding the behaviour of deep-water animals, especially those targeted by exploitation, is important for conservation. For example, understanding interactions between animals and deep-water fishing gear could inform the design of devices that minimize bycatch. 2. We describe the 'TrapCam', a self-contained, high-definition video system that requires neither the support of a vessel once deployed nor special equipment to deploy or retrieve. This system can record 13-h videos at 1080p resolution and is deployable on any substrata at depths of up to 100 m. The system is inexpensive (<$3000 USD), versatile and suited to the study of animal behaviour at depths inaccessible to scuba divers. 3. We evaluate the performance and cost effectiveness of TrapCam and analyse videos retrieved from pilot deployments to observe spot prawn (Pandalus platyceros) traps at 100 m depth. Preliminary analyses of animal-prawn trap interactions yield novel insights. We provide future directions for researchers to use this type of camera system to study deep water-dwelling species around the world.

The cardiovascular systems of Puget Sound king crabs, Lopholithodes mandtii, and brown box crabs, Lopholithodes foraminatus, were mapped using corrosion casting techniques. Both species have a similar external morphology and a very similar cardiovascular system. Seven arteries (five arterial systems) arise from the heart. The small anterior aorta exits from the anterior surface of the heart and supplies hemolymph to the eyestalks and brain region. The pathway of the two sets of paired arteries, the anterolateral arteries and hepatic arteries, is close, and they intertwine with one another during their initial course. The anterolateral arteries exit from the anterior dorsal surface of the heart and supply hemolymph to the hypodermis, cardiac stomach, antennal gland, and mandibular muscles, whereas the hepatic arteries branch profusely within the hepatopancreas. The lithodids are believed to have evolved from hermit crab ancestors; indicative of these evolutionary origins the posterior aorta is well developed and supplies hemolymph to the large abdomen and the gonads. Exiting from the ventral surface of the heart, the sternal artery is the largest in the system. It branches to supply the mouthparts, chelae, and pereiopods. The differing arrangement of this vessel compared with that of the pagurid anomurans is due to the more carcinized (crab-like) morphological features of the lithodid anomurans. The arrangement of vessels supplying the gills is different compared with that of brachyuran crabs; the infrabranchial sinus joins to the afferent gill vessels at their midpoint, rather than along the ventral edge. In general, the circulatory system of the lithodid crabs is somewhat simpler than that of brachyuran crabs, with fewer branching capillary-like networks. Nevertheless, it is still very complex. In accordance with anatomical descriptions of blue crabs and cancrid crabs it would also seem appropriate to classify the lithodid circulatory system as one that is incompletely closed.

The production of echinoid larvae and juveniles is required in both wild‐population enhancement programs and full life‐cycle culture. Many echinoid species of commercial interest spawn only once or twice a year, however, restricting temporal access to viable broodstock. High‐energy/high‐protein formulated feeds have been used for gonad enhancement of a variety of echinoid species, but the goal of that activity has always been to produce pre‐mature gonads, which the market requires, not the production of mature gonads for breeding. The present investigation, originally established to examine gonad enhancement, took advantage of a spawning event to assess the efficacy of a formulated feed to extend the spawning period or reduce gonad recovery time after spawning in a commercially relevant echinoid, the green sea urchin (Strongylocentrous droebachiensis). Urchins held in suspended sea cages were fed either a formulated, commercial, pelleted urchin diet or bull kelp (Nereocystis luetkeana) over 12 weeks, survival, somatic growth, gonad quantity (wet weight, yield), and gonad quality (presence/absence of gametes) being examined over time. Survivorship after 12 weeks was high, little difference being observed between the two diets (mean ± SE: 98.2 ± 1.1% and 95.9 ± 1.9% for kelp and formulated feed, respectively). There was no significant difference in somatic growth between the two treatments, but formulated feed led to significantly higher gonad wet weight and yield than kelp at the end of the study. When compared with kelp, formulated feed may have led to earlier spawning, quicker gonad recovery, and prevented the complete spawning of all urchins, thus extending the period of gamete availability. Formulated feeds may have the potential to maintain reproductively active broodstock over an extended time, allowing expansion of the period in which echinoid larvae and juveniles can be produced.

California sea cucumbers Parastichopus californicus are reported to prefer hard over soft substrates and can be found associated with shell hash at bivalve farms. We predicted that soft substrates and oyster shells might restrict the movement of sea cucumbers and tested this hypothesis in a laboratory experiment. Small (contracted length, ~4.5 cm) and large (~10 cm) sea cucumbers were placed in the middle of tanks on a uniform, hard substrate (30 × 30‐cm PVC sheet) surrounded by various substrates: no substrate (control); silt, fine sand, and very coarse sand (grain sizes: 2–50 μm, 100–250 μm, and 1–2 mm, respectively); and Pacific oyster Crassostrea gigas shells (~10‐cm border around the PVC sheet) with or without silt surrounding the shells. Movement of individuals was monitored over 24 h in six replicate trials. The mean percent (±SE) of sea cucumbers remaining on the PVC sheet was not significantly different among the control (22 ± 7%), silt (28 ± 8%), fine sand (37 ± 8%), and very coarse sand (20 ± 7%) treatments. Low percentages (<40%) indicated that the animals were not averse to emigrating to the soft substrates. However, significantly more sea cucumbers remained on the hard substrates (PVC and oyster shells) in the treatments comprised of oyster shell (83 ± 7%) and silt with oyster shell (82 ± 8%) than on the PVC sheet in the soft substrate treatments, indicating an affinity of the sea cucumbers for the oyster shells. Significantly more small individuals (95 ± 5%) than large ones (69 ± 9%) remained on the hard substrates. This study demonstrates that soft substrates do not prevent the movement of sea cucumbers under laboratory conditions, while oyster shells may cause a decrease in movement, which has implications for benthic ranching of commercially‐farmed sea cucumbers.