Relationships Between Otolith Growth Increment Widths and Bottom Temperature for Three Bering Sea Flatfish Species
Figure 3. Results of bomb-produced radiocarbon (C-14) age validation studies. The reference is Pacific halibut (line is a LOESS smooth of measured C-14 representing 1944 to 1981). The test species displayed in comparison to the reference are northern rockfish, Dover sole, and yellowfin sole.
Fish growth is affected by environmental variables. In turn, fish otoliths are thought to provide a record of these variables through their link to somatic growth. To explore the effects of climate on fish growth, a dendrochronology (tree-ring science) study was undertaken in collaboration with Dr. Bryan Black (Hatfield Marine Science Center, Oregon State University.)
The dendrochronology technique of cross-dating was applied to fish otolith growth increments. Cross-dating is the process of assigning the correct calendar year to each growth increment and comparing relative growth increment time series, or chronologies, among specimens in a sample set. This technique can be used to evaluate synchrony in growth between individuals of a given species and among different species, and between growth increments and environmental indices.
Digital photographs of otolith cross sections were visually cross-dated to assign the correct calendar year to each growth increment. Growth increment widths were then measured using imaging software. Cross-dating was statistically verified using COFECHA software (International Tree-Ring Data Bank Program Library) to ensure that no growth increments were missed or incorrectly added.
Growth declines associated with age were detrended by fitting each measurement time series to a negative exponential function. Detrended measurement time series were then averaged to obtain master chronologies, or ring-width index time series, for each species.
Master chronologies were developed for three species of Bering Sea flatfish: northern rock sole (Lepidopsetta polyxystra), yellowfin sole (Limanda aspera), and Alaska plaice (Pleuronectes quadrituberculatus). Otolith growth among individuals of a given species was found to be highly correlated (R = 0.59-0.66), as were the master chronologies among the three species (R = 0.71-0.90). The high degree of synchrony between chronologies is a corroboration of age estimates obtained from counting growth increments.
All three master chronologies were highly correlated with summer bottom temperatures (R = 0.59-0.90; Fig. 3 above) and sea surface temperatures (R = 0.71-0.85). Otolith ring width index was positively related to Bering Sea summer bottom temperatures for all three species (R2 = 0.59-0.81).
Given the relationship between otolith size and body size, this study suggests that somatic growth is strongly influenced by environmental factors, either directly (metabolically) or indirectly (e.g., as a result of food availability), and occurs synchronously across species and broad spatial scales in the Bering Sea.
This work will be presented at the Fourth International Otolith Symposium in Monterey, California, in August 2009, and a paper is currently in preparation.
By Beth Matta
Age and Growth Educational Outreach
Age and Growth Program Staff continue to inspire budding young scientists with educational outreach activities. Chris Gburski and Chris Johnston, with assistance from Irina Benson, put on an "Age and Growth of Fishes" demonstration for the 2009 Summer NOAA Science Camp. Craig Kastelle presented a demonstration of marine life using fish otoliths and marine mammal bones at Cedar Wood Elementary School’s annual "Day of Science."
