link to AFSC home page

link to AFSC home page link to NMFS home page link to NOAA home page

Resource Assessment & Conservation Engineering (RACE) Division

AFSC Quarterly
Research Reports
Oct-Nov-Dec 2008
Contents
Feature
Items
ABL Reports
FMA Reports
HEPR Reports
NMML Reports
RACE Reports
REFM Reports
All Reports (.pdf)
Quarterly Index
Quarterly Home

Fisheries Behavioral Ecology Program - Newport Laboratory

Sources of Growth Variability in Age-0 Northern Rock Sole

juvenile northern rock sole
Figure 1.  Juvenile northern rock sole (Lepidopsetta polyxystra).
 

Considerable research effort has been directed at evaluating spatial and temporal patterns in growth rates of juvenile fishes and is often used to define "essential fish habitat," evaluate habitat quality at different sites, and indicate potential future recruitment. Furthermore, understanding the causes of contemporary variation in growth rates can offer insights into the likely consequences of climate change for growth and recruitment of coastal marine fishes.

In conjunction with the AFSC and Oregon State University colleagues, the Fisheries Behavioral Ecology Program (FBEP) examined patterns in growth variability in North Pacific Ocean and Bering Sea fishes through integration of field sampling, laboratory experiments, and modeling. Of particular interest was identifying the sources of environmental variability contributing to variable growth of larval and juvenile stages and quantifying their relative impacts.

In a recently completed study, Thomas Hurst and colleagues examined the abundance patterns and growth dynamics of age-0 northern rock sole (Lepidopsetta polyxystra) (Fig. 1) over 4 years (2004-07) in three Kodiak Island nursery areas (Holiday Beach in Middle Bay, Pillar Creek Cove in Monashka Bay, and Shakmanof Beach in Shakmanof Bay).

Following the settlement period, fish were sampled monthly (July-October) with a 3-m beam trawl at a series of fixed-position transects at each site. Growth rates of age-0 northern rock sole were based on observed increases in mean size between monthly sampling dates. Additionally, "Realized Growth" (RG) expressed the rate of observed growth in the field relative to maximum potential growth based on prevailing water temperatures.

  figure 2, see caption
Figure 2.  Growth rates of age-0 northern rock sole in three Kodiak Island embayments, 2004-2007.  Symbols are mean length ± standard error of fish all fish in sample.  Triangles–Holiday Beach; Squares – Pillar Creek Cove; Inverted triangles – Shakmanof Beach.
 

Temperature recorders were placed at each site to determine local spatial variation, and a long-term record was used to describe regional inter-annual variability and serve as a benchmark for site-specific comparisons. Site-specific temperature regimes were converted to potential growth rates based on previously established relationships.

The results of this study offer new insights into the role that temperature variation plays in the early life history of Gulf of Alaska northern rock sole.

Average size of northern rock sole in mid-July (following the settlement period) ranged from 21.7 to 35.1 mm and was positively related to regional temperatures in the preceding winter and spring, suggesting that temperature may be regulating the timing of spawning and larval growth rates. Further, variation in size among sites was less than that observed among years, indicating the importance of regional pre-settlement conditions.

Summer growth on the nursery grounds varied significantly among sites and years, with average length of age-0 fish in mid-September ranging from 38.2 to 63.1 mm. Contrary to expectations of density-dependence and thermal regulation, nursery ground growth rates (expressed in mm·day-1 or RG) were not significantly correlated with fish density or water temperatures.

Fish at the Holiday Beach site exhibited the highest growth rates in all 4 years of sampling (Fig. 2) despite the high inter-annual variance in fish density observed at this sight. Growth was generally slowest at the Shakmanof Beach site. While temperatures were slightly lower at this site, thermal differences were insufficient to account for growth differences.

Application of observed variation in single parameter perturbation models of growth was used to quantify the relative contributions of variation in post-settlement size, RG, and thermal regime to first-year growth. The minor contribution of thermal variation to summer growth rates appears related to the comparatively low thermal sensitivity of northern rock sole.

Average temperature varied 2.0oC among years, corresponding to a 10.3% increase in growth potential, or a cumulative potential increase of only 3.6 mm over the course of a 100-day growing season. Variation in realized growth rates varied systematically among years and sites and declined during the course of the growing season, possibly reflecting the conservative growth strategy of this cryptic species.

Interestingly, the size variation observed following settlement in mid-July persisted through the growing season and accounted for over 50% of the body size variation observed by mid-September. These results suggest that climate changes influencing spawning time and larval growth may have larger impacts on first-year growth and recruitment of this species than temperature effects on the growth of nursery-resident juveniles.

Future work by FBEP researchers will examine patterns of prey availability and predator exposure to further refine biotic controls on fish growth. In addition, variability in fish condition and lipid content will be compared with growth rate patterns. Finally, the patterns observed at these sites will be contrasted with patterns in other parts of the species range.

by Thomas Hurst
 

<<<previous

next >>>


            Home | FOIA | Privacy | USA.gov | Accessibility      doc logo