Growth and mortality underpin all populations, including those we harvest
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Early life history matters!
The early life history phase is vitally important to shaping both an individual's future prospects in life, but also shaping current and future population trends. Subtle changes in growth and mortality rates during the early life history phases can have drastic implications for future population size and structure. However, we know very little about the growth and mortality processes that occur during the egg, larvae and juvenile phases, despite their great importance. Fortuitously, the otoliths of fish contain a wealth of information regarding age and growth. However, interpreting this information correctly is complex. Validation studies are central to aiding the interpretation of this information.
This study was published in Journal of Fish Biology. |
Food and Temperature
Careful measurements of fish growth were essential to validating backcalculation models
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Food supply and temperature both impact greatly on the growth of fish. Generally, higher temperatures lead to faster growth, however this is dependent on sufficient food being available to support growth. Conversely, metabolic costs are higher at warmer temperatures, hence the effects of starvation may be greater under warmer conditions, than cooler. During periods of starvation, fish can stop growing, or even shrink. However, detecting these transient effects is problematic, despite their great importance in shaping the live history of individuals, cohorts, and populations.
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Back calculation
Much time was spent behind a microscope, measuring the growth increments in tiny fish otoliths
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Growth backcalculation is a technique for estimating the size of a fish at specific points in its life history, using the information present in its otoliths, bones or scales. This is based on the premise that growth rings present in these hard structures grow in proportion with the size of the animal, such that they can be used to infer past size. In this study, I determined that backcalculation using growth rings in otoliths is very accurate, except during periods of starvation. During this time, fish can shrink in size, yet their otoliths continue to grow, resulting in an uncoupling of the otolith-somatic growth relationship. Future studies should look to combine information on growth and mortality processes in addition to marking of fish to explore the influences of dispersal on growth and mortality in natural systems.
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Fish grown under a range of food and temperature regimes exhibited highly variable growth histories. Larval moggies grown at 28 degrees (red lines) grew faster, but were more responsive to changes in food supply. Conversely, moggies grown a 24 degrees (blue lines) showed no differing responses to food supply. As such, strong interaction effects exist between food supply and temperature.
Starrs, D., Ebner, B.C., and C.J. Fulton (2013) Can backcalculation models unravel complex larval growth histories in a tropical freshwater fish? Journal of Fish Biology 83: 96-110 doi: 10.1111/jfb.12152 LINK
