There and Back Again: A Blueback's Tale
If you've been an active reader of our blog or have kept up with our research and restoration work, you may be aware that river herring refers to two species: alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis). This is done mostly because they are so similar in appearance - and hence, very difficult to tell apart - and because they have similar life history characteristics. Yet differences do exist. Alewife are typically more abundant in the northern part of their range that includes the entire Atlantic coast; while within spawning rivers, blueback herring typically travel further upstream to spawn. Morphologically, alewife have slightly larger eyes and a grey-green dorsal side (back), while blueback herring have a more blue-green back (hence the name I'm assuming). Yet the most foolproof way to tell them apart is by the color of their peritoneum, the membrane that surrounds their abdominal cavity. Alewife have a pale white peritoneum, while blueback herring have a black peritoneum. Unfortunately, the only way to see this membrane is to cut them open, which is why we only do this to the few river herring we find dead in our nets each year.
Since we started our monitoring in 2014, all herring checked in this way have been alewife, including both adults and juveniles/young-of-year. And a blueback herring hasn't been recorded in Wreck Pond since 2006, when two were caught by Capt. Al Modjeski as part of a prior study. That is, until today.
As we approached our net this morning, we discovered a headless herring lying on the pond bank. After processing the living fish in our net (which included white perch, gizzard shad, American eels, white suckers, brown bullhead, pumpkinseeds, bluegills, and 11 river herring) we cut open the headless herring expecting to see a pale peritoneum confirming it as an alewife. However, we were shocked and excited to see otherwise. A bold, black peritoneum signified this fish as a blueback herring, something we haven't seen in here in 15 years. It appears, blueback herring are back in Wreck Pond.
Now to the nature of its headless appearance. The ragged look of the wound suggests the alewife was preyed upon by another organism. There has been a sighting of a river otter in Wreck Pond this year, and we observed river otter tracks on the beach last summer. Otters are known to eat fish head first, and accounts exist from fishermen from early in the last century of their nets being raided by otters and having an entire catch headless as a result. Perhaps our headless fellow suffered the same fate. We don't know, but we are excited to continue monitoring this year and see what else we can learn.