Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


White Marlin (Kajikia albida) is a highly migratory species that occurs throughout temperate and tropical regions of the Atlantic Ocean and is the basis of a large sport fishery along the United States Atlantic coast. The single, Atlantic-wide stock is considered to be overfished, with less than one-third the spawning biomass estimated to be necessary for maximum sustainable yield. Billfish management measures adopted by the International Commission for the Conservation of Atlantic Tunas (ICCAT) and implemented in the U.S. by the National Marine Fisheries Service (NMFS), as well as increasing angler awareness of conservation, have resulted in the vast majority of White Marlin being released after capture. In 2003 it was estimated that more than 99% of the 4,000-8,000 White Marlin captured each year in the U.S. recreational fishery are released alive. Recent research aimed at estimating the rate of post-release mortality suggests that it may vary with hook type, hook location, angling time, air exposure, relative temperature change, and the size of the fish. Stress resulting from an angling event may also have sublethal physiological effects that negatively impact growth rates, reproductive output or investments, ability to evade predators, and disease resistance. I examined post-release mortality and post-angling physiological stress by collecting physiological data from blood samples and deploying pop-up satellite archival tags (PSATs) on recreationally angled White Marlin. Over two field seasons blood samples were collected from 68 recreationally caught White Marlin of which 22 were tagged with PSATs distributed over three stratified angling-time categories: short (0-10 min, n=8), medium (10-20 min, n=7), and long (>20 min, n=7). Plasma glucose, sodium, and cortisol increased significantly with fight time, plasma potassium decreased significantly with fight time, and plasma lactate and chloride increased significantly with fight time and water temperature. Habitat utilization following release was not affected by physiological status, angling time, lower jaw fork length (LJFL), or sea surface temperature. These results demonstrate that increased angling times and warmer water result in greater physiological stress in White Marlin. A 21% post-release mortality rate was inferred from PSAT data, and if non-reporting and early releasing tags are additionally assumed to be mortalities, post-release mortality could be as high as 32%. Post-release mortality was not related to fight time, LJFL, or sea surface temperature and was marked by elevated plasma potassium concentrations regardless of which mortality scenario was assumed. My estimates of post-release mortality rates in this study were more than an order of magnitude higher than had been previously assessed for White Marlin caught on circle hooks. This disparity in estimates may indicate that either blood sampling, removing fish from the water, or some combination of the two greatly increased post-release mortality. In order to maintain low rates of post-release mortality anglers should not remove White Marlin from the water and should resuscitate fish regardless of angling time.



© The Author