Latitudinal and Cross-Shelf Patterns of Size, Growth and Mortality of a Tropical Damselfish Acanthochromis polyacanthus on the Great Barrier Reef

Abstract

Patterns of age and growth of a sedentary damsel fish Acanthochromis polyacanthus were tested over a latitudinal range of approximately 10 degrees (1,200 km) on the Great Barrier Reef, Australia. Within latitudes these patterns were also compared on reefs across a continental shelf that ranged in width from 52 to 128 km. Although variation in length-max, growth, age-max and the von-Bertalanffy metrics of L, and K were found within and among latitudes, greatest variation in some demographic characteristics were found across the shelf regardless of latitude. Fish were always smaller at inner shelf reefs and grew more slowly when compared to mid and outer shelf reefs. The oldest fish collected was 11 years old and, there were no consistent variation in age-max among distances from shore. On outer reefs, there was a linear relationship with age-max and latitude. This ‘tropical gradient’ of age only explained 34% of the variation, further this was not found when the oldest 10% of fish were considered. Fish only reached an age-max of 6 years on the southern-most reefs. There was a trend for a smaller L with latitude but, it was not significant and L did not vary predictably with water temperature. The sampling of MPAs did not confound the resultant patterns. Instantaneous mortality rates were 0.245-0.685, highest at inner reefs and showed no consistent MPA-related patterns. Our study suggested that the mid and outer shelf waters of the GBR appeared best suited for growth of A. polyacanthus. In conclusion, position on continental shelves and related local environmental conditions needs to be considered in spatial models of growth.

Age and growth of damselfish Chromis notata (Temminck & Schlegel, 1843), Jeju Island, Korea

“…Studies of the ages of tropical pomacentrid fishes have been more common than those of temperate pomacentrids. Maximum ages in the family Pomacentridae determined by otolith analyses include: 10 years for Parma wardi (Fowler & Doherty, 1992); 32 and 27 years for Stegastes arcifrons and S. leucorus beebei, respectively (Meekan, Ackerman, & Wellington, 2001); 11 years for Acanthochromis polyacanthus (Kingsford & Hughes, 2005); 15 years for S. fuscus (Schwamborn & Ferreira, 2002); and as low as 4 years for S. flaviatus from the eastern Pacific Ocean (Meekan et al, 2001). Age T A B L E 2 Likelihood tests comparing von Bertalanffy growth parameters by non-linear regression estimates for Chromis notata (1) females and (2) groups estimated here for C. notata are younger than the maximum ages determined for other pomacentrid fishes.…”

Latitudinal and Cross-Shelf Patterns of Size, Age, Growth, and Mortality of a Tropical Damselfish Acanthochromis polyacanthus on the Great Barrier Reef

“…Spatial variation in the demographics of cross-shelf populations of A. polyacanthus was determined using a partially hierarchical sampling design. Individuals of a wide range of sizes were collected from two or three sites (separated by 100s of meters within a reef) from two or three replicate reefs within each of three distance strata (inner, mid, and outer shelf) spanning the width of the continental shelf at three latitudes, Lizard Island, Townsville, and the Whitsundays (Townsville data are from Reference [26]). Variation in fish demographics over a broader latitudinal range was achieved by sampling additional outer shelf reefs located in the Swains, and the Capricorn section in the GBR (Figure 1, Table 1).…”

“…Alternating translucent and opaque increments were interpreted as annuli. This was previously validated by Kingsford and Hughes [26]. Sections were coded and examined in random order, and the opaque increments were counted on two occasions by the same observer separated by four days.…”

“…Furthermore, a high abundance of predatory fishes could affect patterns of abundance of prey and the size/age and growth characteristics of reef-based populations (e.g., Reference [5]). Kingsford and Hughes [26] found great differences in size maxima and von Bertalanffy characteristics of fish across the shelf, where fish from inner reefs were much smaller. However, this project did not test for variation in demographic characteristics with latitude.…”

“…Environmental influence on growth, therefore, would be highly localized as no broad-scale movements are undertaken. The documented age maximum of the species is 11 years [26].…”