TEMPERATURE EFFECTS ON OTOLITH MICROSTRUCTURE AND BIRTH MONTH ESTIMATION FROM OTOLITH INCREMENT PATTERNS IN ATLANTIC MENHADEN

We demonstrate temperature-influenced increment spacing in the sagitta l otoliths of juvenile Atlantic menhaden Brevoortia tyrannus reared at different temperatures and describe otolith increment patterns from w ild juveniles born in different months. Tank-reared individuals comple ted metamorphosis a month earlier at 25 degrees C than at ambient temp eratures (10-14 degrees C). We identified several patterns from the se ctioned otoliths, including reduced time to metamorphosis, faster tran sition to the juvenile stage, and increased increment spacing after on set of metamorphosis for those individuals exposed to warmer temperatu res. For wild individuals that could be accurately aged, mean otolith increment spacing in the zone from 70 to 80 increments increased 1-2 m u m for fish born in November and December to more than 3 mu m for fis h born in February. The increase in increment spacing is consistent wi th the arrival of individuals across seasonally warming temperatures i n the estuary. A discriminant analysis based on otolith increment spac ing and metamorphic patterns successfully classified birth month for 5 9-100% (65% overall) of Atlantic menhaden spawned between November-Feb ruary. This approach is being developed ultimately to identify the bir th month of wild Atlantic menhaden adults in order to test fur differe ntial survival among cohorts born in different months that recruit to the fishery.