Robert W. Hannah

Buoyancy regulation and barotrauma in two species of nearshore rockfish

Abstract Fishes with closed swim bladders regulate buoyancy during depth changes by secreting and resorbing swim bladder gases. Forced ascent during fishery capture results in barotrauma caused by rapid expansion and exsolution of gases from body fluids. Pressure changes in hyperbaric chambers were used to examine changes in swim bladder integrity and acclimation rates in two ecologically different, yet congeneric, species: Black rockfish Sebastes melanops and China rockfish S. nebulosus. We also conducted simulated-capture experiments to investigate the relationship between capture in a fishery, barotrauma from pressure change, and survival after release. Black rockfish acclimated faster than China rockfish to both increases and decreases in pressure, but both species were much slower to acclimate than other physoclists, such as Atlantic cod Gadus morhua. Black rockfish required up to 48 h to acclimate from 4 atmospheres absolute (ATA; depth equivalent of 30 m) to surface pressure and required up to 168 ...

Behavior of Nine Species of Pacific Rockfish after Hook-and-Line Capture, Recompression, and Release

Abstract We evaluated the effect of barotrauma on the behavior of nine species of Pacific rockfish Sebastes spp. after hook-and-line capture and release using a video-equipped underwater release cage. Sampling was conducted across a range of bottom depths (12–194 m), mostly where barotrauma resulting from an expanded swim bladder and gaseous release of dissolved blood gases would be expected. Behavioral impairment from barotrauma was depth related but highly species specific. Increased depth of capture was associated with lower behavioral scores for black rockfish S. melanops, blue rockfish S. mystinus, and yelloweye rockfish S. ruberrimus, but not for canary rockfish S. pinniger. Behaviorally impaired fish showed a decreased ability to maintain vertical orientation and were slower in exiting the release cage. Species differed in the degree of behavioral impairment resulting from barotrauma and in how rapidly behavioral impairment increased with depth of capture. When captured at depths between 40 and 99 ...

Escaping the Surface: The Effect of Capture Depth on Submergence Success of Surface-Released Pacific Rockfish

Abstract We evaluated the effect of capture depth and fish size on the ability of several Pacific rockfishes Sebastes spp. to resubmerge after hook-and-line capture and surface release. We observed fish as they were released into a bottomless floating enclosure, and we recorded submergence success within a 5-min time limit. Submergence success was greater than 80% for all rockfish captured in depths less than 30 m. Yellowtail rockfish S. flavidus (N = 51) were 100% successful at submerging in less than 49 s at all depths sampled (10–51 m). At capture depths of 40–51 m, submergence success was 89% for quillback rockfish S. maliger (N = 9), 65% for black rockfish S. melanops (N = 46), and 30% for canary rockfish S. pinniger (N = 40). At depths of 30–51 m, submergence success was 32% for blue rockfish S. mystinus (N = 31). The external signs of barotrauma (e.g., exopthalmia, eversion of the esophagus) increased with depth of capture and were least prevalent in yellowtail rockfish and quillback rockfish. The ...

Discard Mortality of Trawl-Caught Lingcod in Relation to Tow Duration and Time on Deck

Abstract The lingcod Ophiodon elongatus is a benthic marine fish commonly caught by groundfish trawlers and discarded due to low catch limits. Managers must account for the mortality of bycatch to assess population status accurately. Our objectives were to estimate the actual mortality of trawl-discarded lingcod (50–84 cm) and describe their physiological stress response to capture. We investigated three major factors of the trawling operation that may influence lingcod survival: tow duration, fish size, and the amount of time fish were on the deck of the vessel. Survival was monitored for 21 d and each surviving animal was then physically and physiologically evaluated. The results showed that regardless of the duration of the tow, lingcod survival was 100% for animals discarded immediately after the cod end was emptied on deck. All lingcod captured during a tow of average commercial duration demonstrated a maximal stress response, measured by plasma cortisol, glucose, and lactate concentrations. As expec...

Site Fidelity and Movement of Eight Species of Pacific Rockfish at a High-Relief Rocky Reef on the Oregon Coast

Abstract We used acoustic telemetry techniques to study the movements of eight species of Pacific rockfish (genus Sebastes) inhabiting Siletz Reef, a high-relief rocky reef complex on the Oregon coast. Our primary interest was evaluating potential residence times for rockfish species in small, no-take marine protected areas (MPAs) like those recently designated for Oregon waters (337–1,502 ha). We tagged 6 black rockfish S. melanops, 31 canary rockfish S. pinniger, 9 yelloweye rockfish S. ruberrimus, 5 quillback rockfish S. maliger, and 2 copper rockfish S. caurinus, along with single specimens of china rockfish S. nebulosus, vermilion rockfish S. miniatus, and tiger rockfish S. nigrocinctus, and monitored their movements with a large (about 5,200-ha) receiver grid for over a year. Canary rockfish showed low site fidelity and wide-ranging movements that exceeded the scale of our detection grid and a wide range of vertical movements (up to 27 m). Quillback, vermilion, tiger, china, and some yelloweye rockf...

Evaluation of a Selective Flatfish Trawl and Diel Variation in Rockfish Catchability as Bycatch Reduction Tools in the Deepwater Complex Fishery off the U.S. West Coast

Abstract We tested the potential of a selective flatfish trawl to reduce bycatch of slope rockfish in the upper continental slope bottom-trawl fishery (250–500 m) on the U.S. West Coast. The trawl we tested differed from typical slope trawls in that it was a low-rise, two-seam trawl with a severely cut back headrope. We used an alternate haul, randomized block design to compare catches of the experimental trawl with those of a typical four-seam, high-rise trawl and to examine diel changes in catch rates for both trawls. The experimental trawl produced catches similar to the control trawl for all commercially valuable flatfish, except arrowtooth flounder Atheresthes stomias, which was reduced 24%. Catches of most rockfish and roundfish were significantly reduced in the experimental trawl (50–94% depending on species). However, the catches of darkblotched rockfish Sebastes crameri and redbanded rockfish S. babcocki were not reduced significantly in the experimental trawl. Nighttime catches were reduced 30–9...

Use of a Novel Cage System to Measure Postrecompression Survival of Northeast Pacific Rockfish

Abstract We used a caging system designed to minimize the adverse effects of caging fish in marine waters to evaluate the discard mortality of seven species of rockfish Sebastes with barotrauma. Altogether, 288 rockfish were captured, scored for barotrauma, evaluated behaviorally at the surface, and caged individually on the seafloor for 48 h to determine survival. With the exception of three blue rockfish S. mystinus, the condition of surviving fish after cage confinement from 41 to 71 h was excellent. At capture depths up to 54 m, survival was 100% for yelloweye rockfish S. ruberrimus (n = 25) and copper rockfish S. caurinus (n = 10) and 78% for blue rockfish (n = 36). At capture depths up to 64 m, survival was 100% for canary rockfish S. pinniger (n = 41) and quillback rockfish S. maliger (n = 28) and 90% for black rockfish S. melanops (n = 144). Black rockfish survival was negatively associated with capture depth (m) and the surface-bottom temperature differential (°C). Blue rockfish survival was negatively associated with capture depth. Barotrauma signs and surface behavior scores were not good indicators of survival potential across species but were useful within species. In black and blue rockfish, severe barotrauma was negatively associated with survival, while higher scores on reflex behaviors at the surface were positively associated with survival. The high survival rates and excellent condition of some species in this study suggest that requiring hook-and-line fishers to use recompression devices to help discarded rockfish return to depth may increase survival for some species.

Spatial Changes in Trawl Fishing Effort in Response to Footrope Diameter Restrictions in the U.S. West Coast Bottom Trawl Fishery

Abstract Changes in the spatial distribution of U.S. west coast bottom-trawl effort in relation to areas of prime habitat for rockfish Sebastes spp. were evaluated between 1992 and 2001. Prime trawlable rockfish habitat (PTRH) was defined based on the spatial distribution of high rockfish catches from logbook data for 1992-1995. Bottom-trawl effort was sharply reduced within PTRH after the establishment of maximum trawl footrope diameter restrictions in 2000. However, reductions in rockfish catch limits prior to 2000 had already reduced trawl activity within these areas, confounding the effects of reduced trip limits and footrope diameter restrictions. Fishing inside PTRH rebounded in 2001, when retention limits for yellowtail rockfish Sebastes flavidus as flatfish bycatch were raised, suggesting that limits may be as important as gear restrictions in determining the spatial distribution of trawl effort in this fishery. The untrawled area of PTRH between 43°N and 48°N in 2000-2001 was estimated at about 1...

A comparison of yield per recruit and revenue per recruit models for the Oregon ocean shrimp, Pandalus jordani, fishery

Fishery regulations for Oregon ocean shrimp, Pandalus jordani, are designed to protect age 1 shrimp from overharvest and sustain long-term fishery benefits. Designing appropriate management regulations including minimum mesh size and season dates is complicated by the interaction of natural mortality, fishing mortality, and market factors including prices and revenues. The effects of these variables on management strategies were evaluated using yield per recruit and revenue per recruit models. The model that maximized yield indicated that an early season-opening date was optimal; however, due to size dependent ex-vessel prices, the revenue model suggested that a season-opening delay could generate higher total revenues, while decreasing total effort and total harvest. These results demonstrate that, depending on management objectives, incorporating market information may have a significant effect on selection of regulatory controls in this fishery.

Measuring the height of the fishing line and its effect on shrimp catch and bycatch in an ocean shrimp (Pandalus jordani) trawl

Abstract The relationship between fishing line height (FLH), shrimp catch and bycatch in a semi-pelagic ocean shrimp ( Pandalus jordani ) trawl was investigated using a newly developed recording inclinometer. The inclinometer was effective at measuring FLH and indicating trawl performance deficits. FLH was determined to be stable during a haul and also between hauls within a given footrope and groundline configuration. FLH was readily adjusted with simple modifications to the footrope “dropper” chains. Inclinometer data showed that FLH can be unequal between double-rigged nets of identical configuration. Shrimp catch and the bycatch of flatfish and juvenile rockfish varied inversely with FLH, suggesting FLH can be adjusted to equalize the catch of shrimp, flatfish and juvenile rockfish between two double-rigged shrimp nets.