Diet Analysis of Potomac River Blue Catfish. Implementation Team Meeting June th Annapolis, Maryland

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Clare Dixon
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1 Diet Analysis of Potomac River Blue Catfish M a r y G r o v e s 1, T i m G r o v e s 1, J o s e p h L o v e 2, B r a n s o n W i l l i a m s 1, R o s s W i l l i a m s 1 1 M a r y l a n d D e p a r t m e n t o f N a t u r a l R e s o u r c e s, I n l a n d F i s h e r i e s C e d a r v i l l e F i s h H a t c h e r y, R R 4, B o x E, B r a n d y w i n e, M D M a r y l a n d D e p a r t m e n t o f N a t u r a l R e s o u r c e s, I n l a n d F i s h e r i e s T a w e s S t a t e O f f i c e B u i l d i n g B 2, T a y l o r A v e, Sustainable A n n a p o l ifisheries s, M D 2 1Goal Implementation Team Meeting June th Annapolis, Maryland

2 PIs: Mary Groves, Tim Groves, Joseph Love, Branson Williams, Ross Williams Partners: Smithsonian Environmental Research Center

3 Rationale: The diet of Blue Catfish in the Potomac River is unknown. Determining diet is essential to better understand potential impact of this growing population. Objective: Identify food resources used by Blue Catfish in the Potomac River.

4 Approach: Since 2008, Blue Catfish from Maryland s portion of the tidal Potomac River have been collected. In addition to basic biological data, gut contents were sorted and identified to the lowest possible taxon.

5 Preliminary results ( ): N= 880 fish (3g 30kg) 39% empty or well-digested matter Fish use shallow water habitats (e.g. Tesselated darters, Bluegill sunfish frequently observed in guts) Clupeids comprise ~ 10% of diet (7% gizzard shad) Potential relevance/impacts: Gain an understanding of species most affected by the presence of Blue Catfish, either through predation or competition.

6 The Blue Catfish diet study will continue on the tidal Potomac River. MDDNR has worked with the Smithsonian Environmental Research Center to collect unidentifiable gut contents for DNA bar coding. The results of this process will help close the gap on the list of fish that are utilized by Blue Catfish The continuation of the annual Blue Catfish survey will enable the examination of temporal shifts in growth and density and will allow further comparisons of the Potomac River Blue Catfish population with other river systems.

7 Methods Fish* collected primarily using low-frequency electrofishing, but also hook-and-line : gastric lavage and fish returned to water 2010 present: fish sacrificed and dissected (also take otoliths for aging studies, gravid ovaries, etc.) *target fish > 610mm TL (primarily piscivorous)

8 Results N= 880 fish (size range; 3 g 30 kg) Many fish are not captured actively feeding (39% guts empty or well-digested matter) Initial data does not show a high number of clupeids in blue catfish guts. Data does show a surprising number of white perch being used as a food source. Blue Catfish are generally believed to be a deep water species but examination of stomach contents show that they frequently utilize shallow water species for food. This adds a new perspective to their possible impact on other fish species.

Factors Affecting Rate of Food Consumption

Factors Affecting Rate of Food Consumption Factors Affecting Rate of Food Consumption Prey density (availabilty) Attack rate Handling time Learning, switching, microhabitat selection Functional Response: