May/June Update

Greetings,

Our apologies for the delayed update, but rest assured we’ve been hard at work catching and processing fish. We’ve now completed three monthly nighttime sampling surveys netting a total of 62 trout. Though preliminary, our night sampling does appear to be paying off. Based on 153 stomachs collected at fixed long-term stations during the day and night, we see that peak stomach fullness (i.e. the weight of the prey divided by the weight of the spotted trout) occurs in the early morning, declines to a minimum in the late afternoon, and ramps back up towards sunset (Figure 1). This supports the idea that peak foraging occurs in the early morning hours. As we collect more stomachs, we hope to separate stomach fullness values into smaller time-periods in order to refine peak feeding times.

 

Figure 1. Pooled percent stomach fullness of spotted seatrout over 24-hr period

Over the last several months, we also observed a shift in spotted seatrout diet. Trout stomach contents during March and April were dominated by fish (93% weight), while stomach contents during May and June consisted of both shrimp (56% weight) and fish (43% weight; Figure. 2). 

 

Figure 2. Bi-monthly diet composition of spotted seatrout

Between these two time periods, we also observed a shift in the dominant prey species. Mullet (Mugil sp.) was the dominant fish genera consumed during March and April and comprised 61% by weight of all the fish prey. However, the primary fish species consumed by trout in diet in May and June was menhaden (Brevoortia patronus; at 20% weight) followed by pinfish (Lagadon rhomboides; 12% weight) (Figure 3). Combined, menhaden and pinfish made up 72% of the weight for fish prey. The increase in shrimp consumed by spotted seatrout was dominated by white shrimp (Litopenaeus setiferus) followed by unidentified penaeid shrimp (either white or brown) and brown shrimp (Farfantepenaeus aztecus; Figure 3). White shrimp represented nearly a quarter of all prey groups based on weight.  The percent weight of both unidentified penaeid shrimp and brown shrimp were similar at 13% and 11%, respectively.

 

Figure 3. Prey composition of spotted seatrout diet (% weight)

The dietary changes we’ve observed over the past four months likely reflect a seasonal shift in prey abundance, so it will be interesting to see what the next several months have in store. Our July sampling trip is tentatively scheduled for later this week, and we will do our best to provide frequent updates as we move forward. Feel free to contact us if you have any questions/comments before our next update. Once again, we thank each of our supporters. Without you, this work would not be possible. 

Best,

Chris and Justin