What makes fish vulnerable to capture by hooks? A conceptual framework and a review of key determinants

Considerable time and money are expended in the pursuit of catching fish with hooks (e.g., handlining, angling, longlining, trolling, drumlining) across the recreational, commercial and subsistence fishing sectors. The fish and other aquatic organisms (e.g., squid) that are captured are not a random sample of the population because external (e.g., turbidity) and underlying internal variables (e.g., morphology) contribute to variation in vulnerability to hooks. Vulnerability is the probability of capture for any given fish in a given location at a given time and mechanistically explains the population‐level catchability coefficient, which is a fundamental and usually time‐varying (i.e., dynamic) variable in fisheries science and stock assessment. The mechanistic drivers of individual vulnerability to capture are thus of interest to fishers by affecting catch rates, but are also of considerable importance to fisheries managers whenever hook‐and‐line‐generated data contribute to stock assessments. In this paper, individual vulnerability to hooks is conceptualized as a dynamic state, in which individual fish switch between vulnerable and invulnerable states as a function of three interdependent key processes: an individual fish's internal state, its encounter with the gear, and the characteristics of the encountered gear. We develop a new conceptual framework of “vulnerability,” summarize the major drivers of fish vulnerability, and conclude that fish vulnerability involves complex processes. To understand vulnerability, a shift to interdisciplinary research and the integration of ecophysiology, fish ecology, fisheries ecology and human movement ecology, facilitated by new technological developments, is required.     

马尔代夫海域金枪鱼延绳钓渔场大眼金枪鱼生物学特性

根据2003年12月16日至2004年6月8日马尔代夫水域金枪鱼延绳钓渔获物生物学测定数据，应用统计与回归的方法分性别分别对296尾大眼金枪鱼（Thunnus obesus）的性腺成熟度、摄食等级、摄食种类、性别比例、叉长分布、叉长与去鳃去内脏的重量（GWT）的关系等进行研究。结果表明，（1）性腺成熟度以Ⅰ、Ⅱ和Ⅴ级为主，Ⅴ级比例最高，占37．50％，其中雄性大眼金枪鱼的性腺成熟度Ⅴ级最多（53．96％），雌性Ⅱ级最多（33．81％）。（2）摄食等级以0、1和2级为主，总计为88．52％。（3）大眼金枪鱼的摄食种类中，头足类（鱿鱼）或杂鱼的出现频率较高，分别占48．36％和24．59％。（4）雄性个体所占比例略高于雌性个体，雄性与雌性个体的性别比例为1．12：1，叉长1．00～1．20m的大眼金枪鱼雌性占52．08％，叉长1．20～1．40m的个体雌性占52．59％，叉长1．40m以上的个体，雌性占35．14％。（5）优势叉长为1．10～1．40m，平均叉长为1．29m。（5）根据幂函数回归所得叉长（FL）与去鳃去内脏的重量（GWT）关系式显示，在叉长小于1．51m时，雌性的去鳃去内脏重量小于雄性的去鳃去内脏重量；而在叉长大于1．51m时，雌性的去鳃去内脏的重量大于雄性的去鳃去内脏的重量。[中国水产科学，2006，13（4）：674—678，649]