Stressed Out Fish

Stress has profound effects on the survival, fitness, and health of fish species. Understanding fishery-related stress is key for managing species.

Scientific Publications

Gallagher, AJ, Serafy, JE, Cooke, SJ, Hammerschlag, N (2014) Physiological stress response, reflex impairment, and survival of five sympatric shark species following experimental capture and release. Marine Ecology Progress Series doi:10.3354/meps10490.

Cooke SJ, Hogan ZS, Butcher PA, Stokesbury MJW, Raghavan R, Gallagher AJ, Hammerschlag N, Danylchuk AJ. (2014) Angling for endangered fish: Conservation problem or conservation action? Fish and Fisheries doi:10.1111/faf.12076.


In many fisheries around the world, a portion of the catch is almost always released. But what happens to that fish after it disappears out of sight? And what about the status of it when it was brought in? These are important questions, and quantifying the effects of capture and release on fish survival is critical for determining which practices are sustainable. This is especially important for threatened species, such as sharks, which are caught as bycatch worldwide and have also become popular in recreational catch and release fishing.

Using a standardized fishing technique, we studied the sublethal (blood physiology and reflex impairment assessment) and lethal (post-release mortality with satellite tags) outcomes of fishing stress on 5 species of coastal sharks (great hammerhead, bull, blacktip, lemon, and tiger). We detected species among species in whole blood lactate, partial pressure of carbon dioxide, and pH values. Lactate was significantly with lactate emerging as the sole affected by increasing hooking duration and shark size. We also ranked each species according to degree of stress response, from most to least disturbed, as follows:

Hammerhead Shark > Blacktip Shark > Bull Shark > Lemon Shark > Tiger Shark

We also tagged animals to look at their post-release survival, and we found that nearly 100% of all tracked tiger sharks reported for at least 4 wk after release, which was significantly higher than bull (74.1%) and great hammerhead (53.6%) sharks.

In the Gallagher et al. (2014) paper, we present these fascinating results and discuss which mechanisms may lead to species-specific differences in sensitivity to fishing. In fact, the most basic aspects of the ecology of these 5 different species might be influencing the observed variation in stress responses. This study highlights the notion that certain species (i.e. hammerhead sharks in this study) are inherently vulnerable to capture stress and mortality resulting from fisheries interactions and should receive additional attention in future conservation strategies.

Listen to the PODCAST in the player below. Available for download on SoundCloud.


Catch and release practices are growing in popularity worldwide, and data from this project will be used to determine which fishing methods and guidelines are most sustainable for various species. Furthermore, as protective measures for sharks increase, this project will help identify previously overlooked sources of loss or mortality, thus strengthening future decision-making.


Project Lead:
A.J. Gallagher
Co-investigators & Collaborators:
Dr. N. Hammerschlag
Dr. S. Cooke
Dr. J. Serafy