Sandra L. Diamond

Bycatch quotas in the Gulf of Mexico shrimp trawl fishery: can they work?

Bycatch of unwanted, prohibited, or protected species is a problem in most commercial fisheries. Trawl fisheries are particularly prone to bycatch problems because trawls are not species-selective. In this paper, I review the history of finfish bycatch research in the Gulf of Mexico shrimp trawl fishery and explore the use of quotas to reduce finfish bycatch by examining four fisheries that currently use bycatch quotas: (1) the arrow squid trawl fishery of New Zealand, which uses fleet bycatch quotas for sea lion bycatch, (2) the Alaskan groundfish trawl fisheries, which use fleet quotas under a “vessel incentive program” for prohibited species, (3) the groundfish trawl fishery of British Columbia, Canada which uses individual vessel bycatch quotas for prohibited species, and (4) the multi-species trawl fisheries of New Zealand, which use catch balancing, or individual transferable quotas, for most commercially landed species. Based on the bycatch quota experiences in these fisheries, elements of successful bycatch quota programs include: (1) individual accountability, in the form of individual or cooperative bycatch quotas, rather than fleet quotas, (2) 100% observer coverage, (3) relatively small, manageable fleets, (4) limited landing ports that can be easily monitored, particularly if observer coverage is incomplete, (5) reliable enforcement, (6) penalties that are true disincentives, and (7) some flexibility in the system for fishermen to have alternatives to manage their bycatch. The Gulf of Mexico shrimp trawl fishery, with an estimated 20,000 licensed boats, is currently too large for individual bycatch quotas to be practical, although individual or cooperative bycatch quotas would be excellent strategies for reducing the bycatch of a smaller fleet. Mobile closed areas might be beneficial for reducing the bycatch of particular species, but these short-term closures would require real-time monitoring of bycatch rates and vessel monitoring systems on all vessels. However, under any management regime, incentives and/or rigorously enforced disincentives are the key to successful bycatch reduction.

Using Nested Models and Laboratory Data for Predicting Population Effects of Contaminants on Fish: A Step Toward a Bottom-Up Approach for Establishing Causality in Field Studies

Predicting the effects of contaminants on fish populations is difficult due to their complex life history and high interannual variation in their population abundances. We present an approach that extrapolates laboratory data on contaminant effects, including behavioral effects, to the population level by using a series of nested statistical and simulation models. The approach is illustrated using PCB effects on Atlantic croaker. Laboratory experiments were performed that estimated PCB effects on fecundity, egg mortality, and the swimming speed and predator evasion behavior of larvae. A statistical model converted impaired predator evasion to reduced probability of escaping a predatory fish. An individual-based model then converted the output of the statistical model into changes in larval stage duration and survival, which were used to change elements of the matrix model. A matrix projection model simulated population dynamics for 100 years for baseline conditions and for two hypothetical PCB exposure scenarios. PCB effects were imposed in the model by reducing the fecundity of exposed adults, increasing egg mortality, and increasing the larval stage duration and mortality rate. Predicted population effects of PCBs were small relative to the interannual variation. Our analysis is a step toward understanding population responses to stressors and for ultimately establishing causality in field situations.

Linking “Sink or Swim” Indicators to Delayed Mortality in Red Snapper by Using a Condition Index

Abstract The ability of fish to submerge after discarding is often used as a proxy for survival, but this practice underestimates total discard mortality because delayed mortality is overlooked. Fishery managers need a way to link “sink or swim” indicators, or variables observed during capture and release, with delayed mortality rates. We conducted a cage study of red snapper Lutjanus campechanus off the coast of Texas to estimate delayed mortality rates and to find factors that could link immediate and delayed mortality. Immediate mortality (17%) was predicted by the interaction of depth and the difference in temperature between surface and bottom waters. Lactate levels were also significant predictors of immediate mortality in fish whose blood was tested. Delayed mortality (64%) was predicted primarily by a condition index consisting of the presence or absence of injuries, symptoms of barotrauma, and fish behaviors immediately after capture. Specific categories included bleeding, protruding intestines, everted stomach, exopthalmia, the presence or absence of flapping and gilling behaviors, and problems with cage submergence. The majority of fatalities occurred within 24 h after fish were placed in the cages. Our mortality estimates indicate that red snapper discard mortality was significantly underestimated in the 2005 stock assessment for red snapper. The use of indices that relate the condition of an individual fish at capture to its probability of delayed mortality is an excellent method for linking immediate and delayed mortality and will likely be applicable to many species that are subject to catch-and-release fishing.

A host-parasitoid interaction with Allee effects on the host

We explore the addition of Allee effects to single-species discrete-time models with overcompensatory density dependence. When the intrinsic growth rate of the population, r, is large, the population bifurcates into chaos. The population goes extinct if r is either below a threshold level or very large. The model is then used to study host-parasitoid interactions with and without Allee effects in the host. The coexistence of the host and parasitoid populations both depends on threshold levels of r, threshold levels of the host population size, and the parasitoid potential, which is the product of the searching efficiency of the parasitoid for the host, and the fecundity of the parasitoid. The addition of Allee effects has a negative impact on the coexistence of both populations.

Venting or Rapid Recompression Increase Survival and Improve Recovery of Red Snapper with Barotrauma

Abstract Red Snapper Lutjanus campechanus are the most economically important reef fish in the Gulf of Mexico and a heavily targeted fishery. When brought to the surface from deep water, this species often suffers pressure-related injuries collectively known as barotrauma. This trauma results in high discard mortality and has affected recovery of the fishery. In laboratory experiments using hyperbaric chambers, we assessed sublethal effects of barotrauma and subsequent survival rates of Red Snapper after capture events from pressures corresponding to 30 and 60 m deep. We then evaluated the use of rapid recompression and venting to increase survival and improve recovery after release in this controlled environment. Vented fish in simulated surface release and rapid-recompression treatments had 100% survival. Fish released at the surface that were not vented had 67% survival after decompression from 30 m but only 17% survival from 60 m, while nonvented rapidly recompressed fish had 100% survival from 30 m and 83% survival from 60 m. Fish that were vented upon release at the surface showed significantly better ability to achieve an upright orientation and evade a simulated predator. Results showed clear benefits of venting or recompression. Our data also show strong depth effects resulting in increased barotrauma injuries, more impaired reflexes, and greater mortality as depth increases. Overall, our data support venting or rapid recompression as effective tools for alleviating barotrauma symptoms, improving predator evasion, and increasing overall survival.

Quantifying delayed mortality from barotrauma impairment in discarded red snapper using acoustic telemetry

Abstract Red Snapper Lutjanus campechanus is the most economically important reef fish in the Gulf of Mexico, and despite being intensively managed, the stock remains overfished. These fish are susceptible to pressure-related injuries (i.e., barotrauma) during fishing that compromise survival after catch and release. Barotrauma-afflicted fish may not only experience immediate mortality but also delayed mortality after returning to depth. This variability and unknown fate leads to uncertainty in stock assessment models and rebuilding plans. To generate better estimates of immediate and delayed mortality and postrelease behavior, Red Snapper were tagged with ultrasonic acoustic transmitters fitted with acceleration and depth sensors. Unique behavior profiles were generated for each fish using these sensor data that allowed the classification of survival and delayed mortality events. Using this information, we compared the survival of Red Snapper released using venting, nonventing, and descending treatments over three seasons and two depths. Red Snapper survival was highest at cooler temperatures and shallower depths. Fish released using venting and descender tools had similar survival, and both these groups of fish had higher survival than nonvented surface-released fish. Overall, Red Snapper had 72% survival, 15% immediate mortality, and 13% delayed mortality, and all fish suffering from delayed mortality perished within a 72-h period after release. Results from these field studies enhance the understanding of the delayed mortality and postrelease fate of Red Snapper regulatory discards. Moreover, these data support the practice of using venting or descender devices to increase the survival of discarded Red Snapper in the recreational fishery and show that acoustic telemetry can be a valuable tool in estimating delayed mortality.

External Attachment of Acoustic Tags to Deepwater Reef Fishes: an Alternate Approach When Internal Implantation Affects Experimental Design

AbstractImplanting internal acoustic tags is often a preferred method for tracking fish; however, this procedure can present issues with respect to surgical incision that affect experimental design. This is particularly the case when testing for the effects of barotrauma, where the incision for an internal tag would inadvertently “vent” the fish, precluding an “unvented” or control treatment. The rise of barotrauma experimentation has increased the need for methods facilitating this design. Here, we develop and test a novel technique to externally attach acoustic tags, without causing the release of gasses from the fishs body cavity. In addition, this method does not require anesthetics, thereby allowing researchers to eliminate artifacts associated with sedation when trying to more accurately replicate “real-world” fishery conditions. We used accelerometer/depth tags to provide information on how long an externally tagged fish would retain its tag in situ. Changes in acceleration or changes in depth wer...

Population-level effects of density dependence in a size-structured fishery model

A discrete size-structured fishery model is derived to study the population-level effects of the timing of density dependence. The inherent net reproductive number of an individual is the same if the population is assumed to be identical in every way except the occurrence of intraspecific competition. However, total population size may grow without any restriction if density dependence occurs at the second or the third size class. Data of red snapper with Beverton-Holt and Ricker nonlinearities are simulated to make further comparisons. The numerical study indicates that while the population is more resilient if density dependence occurs at the first size class the equilibrium size is larger if density dependence occurs at the second size class.

Accumulation of triclosan from diet and its neuroendocrine effects in Atlantic croaker (Micropogonias undulatus) under two temperature Regimes.

Rising water temperatures due to climate change may increase the uptake and effects of triclosan in aquatic organisms. Our objectives were to investigate the accumulation of dietary triclosan and its neuroendocrine effects in Atlantic croaker, an estuarine fish, under two temperatures and during depuration. A pilot study was used to select a dietary exposure of 50 mg/kg. For 10 days, fish were exposed to one of four diet/temperature treatments (n = 16/treatment): normal diet at 26 °C and 29 °C and triclosan-treated diet at 26 °C and 29 °C. Fish exposed to triclosan at 26 °C accumulated 2.6 mg/kg wet weight on average versus 5.6 mg/kg wet weight at 29 °C. Triclosan exposure significantly impacted reflexes, resulting in the loss of the dorsal fin reflex (DS) in 53% of fish, while temperature and triclosan-temperature interactions were not significant. Triclosan body burden did not significantly predict DS loss. There were no significant differences in thyroid hormone levels among groups. Triclosan-treated fish at 26 °C were fed untreated pellets for 5 additional weeks. Two fish lost the DS during the first depuration week, and no affected fish recovered the reflex. These results have important implications for fish and their predators, as the DS may be important for swimming performance and social patterning.

HARVESTING IN A STAGE-STRUCTURED POPULATION WITH APPLICATIONS TO THE RED SNAPPER IN THE GULF OF MEXICO

We propose deterministic discrete-time, discrete stage-structured population models with harvesting to investigate population persistence and extinction. The mathematical analysis is centered around the inherent net reproductive number of the population. We apply data of the red snapper in the Gulf of Mexico to simulate the models. We use the models to test for a hypothesis proposed by marine biologists by adding a stochastic component to the deterministic systems that simulating pulses of early juveniles from other populations. We conclude that although pulses of early juveniles from other populations can contribute to the stock size of the early juveniles in the Gulf of Mexico, this contribution is insignificant for the adult population. Therefore, the population may still be in danger of extinction since the ocean environment is unpredictable. Other control strategies are needed in order for the population to be harvested annually.