Polly S. Rankin

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 ...

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...

Tag Location and Retention in Black Rockfish: Feasibility of Using PIT Tags in a Wild Marine Species

Abstract Tag and recovery programs can provide valuable information on population size and exploitation rates in fishes. Passive integrated transponder (PIT) tags are ideal for use in such programs because they provide identification of individual fish and are invisible to anglers, circumventing problems with nonreporting of tags. Our objective was to determine whether PIT tags could be used successfully to tag black rockfish Sebastes melanops. We tested tag placement and tag retention using intramuscularly injected PIT tags (12 × 2.1 mm) in 227 black rockfish (25-47 cm); three tag placement sites located outside of the area normally filleted were evaluated. Tag retention for all tag sites was 100% after 49 weeks; however, two fish retained inoperative tags, which possibly sustained damage during the tagging procedure. The results indicated that the best tagging site is ventral and anterior to the origin of the pectoral fin. At this site, tag retention is excellent, risk of infection is low, tag movement ...

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...

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.

Green Sturgeon Physical Habitat Use in the Coastal Pacific Ocean

The green sturgeon (Acipenser medirostris) is a highly migratory, oceanic, anadromous species with a complex life history that makes it vulnerable to species-wide threats in both freshwater and at sea. Green sturgeon population declines have preceded legal protection and curtailment of activities in marine environments deemed to increase its extinction risk. Yet, its marine habitat is poorly understood. We built a statistical model to characterize green sturgeon marine habitat using data from a coastal tracking array located along the Siletz Reef near Newport, Oregon, USA that recorded the passage of 37 acoustically tagged green sturgeon. We classified seafloor physical habitat features with high-resolution bathymetric and backscatter data. We then described the distribution of habitat components and their relationship to green sturgeon presence using ordination and subsequently used generalized linear model selection to identify important habitat components. Finally, we summarized depth and temperature recordings from seven green sturgeon present off the Oregon coast that were fitted with pop-off archival geolocation tags. Our analyses indicated that green sturgeon, on average, spent a longer duration in areas with high seafloor complexity, especially where a greater proportion of the substrate consists of boulders. Green sturgeon in marine habitats are primarily found at depths of 20–60 meters and from 9.5–16.0°C. Many sturgeon in this study were likely migrating in a northward direction, moving deeper, and may have been using complex seafloor habitat because it coincides with the distribution of benthic prey taxa or provides refuge from predators. Identifying important green sturgeon marine habitat is an essential step towards accurately defining the conditions that are necessary for its survival and will eventually yield range-wide, spatially explicit predictions of green sturgeon distribution.