Physiological and behavioral response of the Asian shore crab, Hemigrapsus sanguineus, to salinity: implications for estuarine distribution and invasion

The invasive Asian shore crab, Hemigrapsus sanguineus, is ubiquitous in the rocky intertidal zone of the western North Atlantic. A likely contributor to this colonization is that H. sanguineus is able to handle a wide range of salinities, and is thus more likely to spread through a greater geographic area of estuaries. This study investigated the salinity effects on this animal by observing survival across a range of salinities, the maintenance of hemolymph osmolality under different salinities, and behavioral preference for and avoidance of salinities. H. sanguineus showed high survival across a broad range of salinities, had little change in hemolymph osmolality over a short-term salinity shock, and behaviorally distinguished between salinities when presented with a choice, under both acclimation salinities of 5 PSU or 35 PSU. Such results suggest H. sanguineus has a hardiness for the rapid changes in salinity that happen in the intertidal zone, yet is capable of physically moving to a more optimal salinity. This enhances their competitiveness as an invader, particularly surviving lower salinities that present challenges during high-precipitation events in rocky intertidal areas, and partially explains this species’ dominance in this habitat type

Promoting the Sustainability of the Gulf of Maine Recreational Groundfish Fishery through Discard Mortality Estimation, Mitigation, and Outreach

Recreational fishing (i.e., angling), a popular leisure activity that provides socio-economic benefits to human societies around the world, can represent a significant source of fishing mortality and impact fish populations and marine ecosystems. Although fish are often released by recreational anglers to reduce fishing mortality rates, the efficacy of discarding fish is often criticized given that fish can die from the factors experienced during the capture, handling, and release process (i.e., discard mortality). Despite this recognition, the rate at which fish suffer discard mortality in specific commercial and recreational fisheries is often unknown and difficult to obtain due to logistical constraints, representing a global concern for fisheries management and sustainability. Such is the case in the Gulf of Maine multispecies recreational fishery for groundfish, specifically Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and cusk (Brosme brosme), where, until recently, discard mortality concerns were frequently identified as key sources of uncertainty in stock assessments and management decisions. To this end, my dissertation presents results from three field-based studies and one qualitative survey to address discard mortality knowledge gaps in this fishery. With the use of electronic tagging and survival analyses, I empirically-derived a discard mortality rate of haddock representative of the fishery and generate responsible fishing practices to reduce such mortality risk. Similarly, I used a field-based tagging approach to determine cusk discard mortality, both in its current state in the fishery and with the use of barotrauma mitigations methods (i.e., descending devices). Given the critically-depleted state of the Atlantic cod stock, I conducted a large-scale sampling effort to identify an ideal set of terminal tackle that anglers could use to sustainably target haddock over Atlantic cod while reducing discard mortality in both species. Finally, because managing fish involves managing people and their expectations, I surveyed anglers who target groundfish to determine if their angling behavior would influence their willingness to adopt responsible fishing practices from previous chapters and what channels they use to access angling information. Taken together, my results highlight the socio-ecological complexity of discard mortality and its implications on the current and future sustainability of this recreational fishery

Improved estimation of discard mortality rates with in situ experiments involving electronic and traditional tagging

Reliable estimates of release or discard mortality (DM) rates for recreational and commercial fisheries are necessary for robust assessment of the effects of fishing on populations and for establishing effective regulatory measures concerning the release of fish. In situ experiments involving the tagging of released fish are most likely to produce accurate estimates given that experimental subjects are captured and released under representative fishery conditions. Data from electronic tags can be used to infer movement or behavioral patterns of released fish, from which mortality times can be derived to then estimate natural mortality and DM rates. However, resulting DM rate estimates are often of low precision (high variance) due to small sample sizes associated with the elevated cost of electronic tags. Alternatively, returns of traditional tags from small scale experiments constitute a relatively inexpensive means of estimating the relative DM rates of two or more groups (e.g., vitality or injury classes, capture methods) of released fish. Combining the two approaches when there are two or more groups of discarded individuals can be beneficial. First, results from the two methods can be used to assess whether experimental effects such as tag-related mortality could bias estimates of DM rates. Second, we propose a modelling approach that integrates data from these two types of tagging methods to produce absolute DM rate estimates that can be more precise than those obtained from electronic tagging alone. We show using simulations under which conditions precision is improved and how different allocations of effort to electronic and traditional tagging can be used to plan DM experiments with respect to the precision of estimates and cost. An example based on a recent study is presented to illustrate the application of the proposed approach