Behavioral Ecology of Color Patterns in Atka Mackerel

Robert R Lauth,Scott W Mcentire,Daniel W Cooper,Jared L Guthridge

doi:10.1577/c09-025.1

Abstract

AbstractThe behavioral ecology of seasonal and ephemeral variations in color patterns of Atka mackerel Pleurogrammus monopterygius was investigated and is discussed relative to alternative mating tactics, reproductive condition, social status, and predation risk. Breeding males underwent a conspicuous seasonal color change during the mating and brooding period, resulting in one of two nuptial phenotypes. Type I males held and defended territories inside nesting colonies and had a uniform yellow coloration with a golden hue across the head and dorsum. Type II males were nonterritorial, hovered above the nesting colony, and attempted periodic forays into the nesting colony; their color was plain yellow with irregular dark blotches across the head and dorsum and a light patch on the nape. When displaced from their nests, type I males also showed dark blotches and a light patch on the nape, but these characteristics were less pronounced than those in type II males. The color of females and nonbreeding males was indistinguishable and exhibited little seasonal variation; however, females close to spawning showed an ephemeral darkening of the body with white spots and patches along the dorsum. Nonbreeding males and females undergoing diel migrations also showed the same pattern across the dorsum but without darkening. The overall mean ratio of males to females in the trawl‐sampled population was 1.22:1.00, of which 44.9% were females, 40% were nonbreeding males, 9.8% were intermediate males (with characteristics intermediate between those of breeding and nonbreeding males), and 5.3% were breeding males. The proportion of breeding males was 12 times higher inside nesting colonies than outside the colonies. The mean fork length (FL) of intermediate and breeding males was larger (by ≤1 cm) than that of females or nonbreeding males. Understanding the behavioral ecology of Atka mackerel is important to the development of a comprehensive ecological index for monitoring and assessing the reproductive health of Atka mackerel stocks.

Highlights

Fish color patterns and associated behaviors are shaped by processes of natural and sexual selection resulting from interactions between fishes and their physical, biological, and social environments (KodricBrown 1998)
Females, nonbreeding males, and intermediate males were present in all trawl catches, whereas breeding males were absent from 55% of the tows; the coefficient of variation (CV 1⁄4 2.44) was highest for breeding males
Male Atka mackerel undergo a seasonal color change during the mating and brooding period, and both sexes can ephemerally alter their color in response to changing social and environmental conditions

Summary

Introduction

Fish color patterns and associated behaviors are shaped by processes of natural and sexual selection resulting from interactions between fishes and their physical, biological, and social environments (KodricBrown 1998). Color patterns and behaviors are used by fishes to communicate vital information about territories, courtship, schooling, and predator avoidance (Endler 1992). Displays a range of color patterns (Rutenberg 1962) and exhibits a variety of complex social behaviors (Nichol and Somerton 2002; Lauth et al 2007a), but no observational studies have previously been conducted in a natural setting to associate Atka mackerel color patterns with behavioral ecology. TABLE 1.—Dates, vessels, methods, locations, and the field collections made for acquiring information on the color patterns and behaviors of Atka mackerel

Methods

Results

Conclusion