The Alaska Fisheries Science Center (AFSC) has a long history of research designed to assess and reduce bycatch mortality of both fish and crabs, with regular funding from the North Pacific Research Board, NOAA's Bycatch Reduction Engineering Program, and other sources. Experiments related to discard practices, bycatch reduction, and fishing gear design have included many collaborative efforts between AFSC biologists in Seattle, Washington; Kodiak, Alaska; and Newport, Oregon; their graduate students; and commercial fishers in Alaska.
The AFSC's Fisheries Behavioral Ecology Program based at Oregon State University's Hatfield Marine Science Center has focused substantial effort on developing ways to assess the likelihood of fish or crab mortality resulting from the various stressors associated with fishing gear encounters and/or animal discard. Reflex Action Mortality Predictors (RAMP), pioneered by AFSC researchers at the Newport lab, have become relatively common tools for estimating likely mortality in North American fisheries. In brief, clear relationships occur between the presence or absence of reflexes, (usually between five and seven different tests) and subsequent delayed mortality of an individual. The relationship is typically described by a sigmoid curve, whereby the probability of mortality increases with the number of lost reflexes, and the species-specific RAMP curves appear to be universal such that there is little variation of effect related to animal gender, size, or type of stress.
Figure 1. Retrieving crab pots in the commercial ocean fishery off Oregon (above) and recreational fishing in Yaquina Bay (below). Only legal sized males are retained while undersize males and all females are discarded.
To date, RAMP curves have been developed by tracking the fates of fishes or crabs held in laboratory or shipboard tanks. Although some laboratory holdings have spanned several months, shipboard holding is necessarily short, and these experiments do not account for some types of mortality that can occur in the natural environment, especially predation on injured individuals. Consequently, the best test of a RAMP curve is a field tag-recovery experiment.
The first RAMP experiments with Dungeness crab were initiated in 2012, with funding from the Oregon Dungeness Crab Commission (ODCC), NOAA's Bycatch Reduction Engineering Program, and an Oregon State University Markham Fellowship to Ph.D. student Noëlle Yochum. In fact, the Oregon Dungeness crab fishery is ideal for a field validation of RAMP, primarily because the likelihood of getting tag returns is high. The Oregon shelf, where the commercial pot fishery is concentrated, is narrow, and the fishing effort during winter and spring months is very high. The inshore recreational fishery is also intensive, and past tag-recovery experiments have yielded returns greater than 30%. In the Dungeness crab fishery all female crabs and all undersized males are returned to the water. The ODCC is required to determine discard mortality associated with the different crab fishing sectors as part of maintaining Marine Stewardship Council certification for their products. Field validation of the RAMP approach with Dungeness crab is perceived as a valid model system for investigations ultimately aimed at the Alaskan crab species.
During 2012, more than 600 crabs were assessed, tagged, and monitored in the Newport seawater laboratories for survival; this yielded the first RAMP data for Dungeness crab. Most of these crabs were collected from commercial pot-fishing operations (nine trips, February through July), and others were gathered from recreational fishers and experimental pot-capture effort in Yaquina Bay, Oregon (Fig. 1). In total, nearly 6,000 crabs intended for discard from the different fishing sectors were assessed for reflex actions. These observations provide the basic information needed to estimate discard mortality, but field validation of the RAMP approach for discard estimation is required.
Figure 2. Undersize Dungeness crab marked with a green T-bar spaghetti tag and released as part of the RAMP field validation experiment. The tag is inserted through the suture at the back of the carapace so that it can be retained through a molt.
RAMP validation depends upon a robust tag-recovery experiment, to provide actual survival data for different RAMP scores. Tag methods have been perfected for Dungeness crab (Fig. 2), and 270 individuals were tagged and released in Yaquina Bay during inshore crabbing trips with recreational gear during fall 2012, and additional crabs will be tagged each month until September 2013. However, the primary tagging effort shifted to the Oregon shelf with the start of the commercial ocean crabbing season at the end of December 2012. Four trips on commercial pot-fishing boats have already been made as of this writing. Crabs will continue to be tagged and released each month during commercial crabbing trips; tag returns already are being recorded with rewards paid to the fishers. Bycatch mortality rates that are generated from the mark-recapture study will be compared to those estimated using the traditional RAMP approach. Tag recoveries also will provide new information on crab movements and insights into ways that fishing practices can be altered to reduce mortality rates of discarded crabs.
By Allan Stoner and Noëlle Yochum (Oregon State University)
