When Pilgrim draws in sea water from Cape Cod Bay for cooling, it also pulls in marine life. The process entrains small marine organisms (e.g., fish and shellfish eggs and larvae) through the system and impinges larger organisms on the intake screens (e.g., adult and young fish and shellfish).

Every six months Pilgrim reports on entrainment and impingement numbers, as well as results from winter flounder tows. Below is a summary of Pilgrim’s 2014 semi-annual reports (Jan – Jun 2014). Read the full reports here:


Thirty-two fish species were found in entrainment samples. Winter-early spring samples were dominated by American Plaice, Yellowtail Flounder, Gadidae-Glyptocephalus, Winter Flounder, Haddock, and Atlantic Cod eggs along with Sand Lance, Grubby, Rock Gunnel, and Shorthorn Sculpin larvae. Late spring-summer collections (May/June) were dominated by wrasse-Yellowtail Flounder, wrasse, Atlantic Mackerel, and Fourspot-Windowpane eggs along with Cunner, Winter Flounder, Sand Lance, and Radiated Shanny larvae. Numbers were mostly consistent with those recorded from 1981-2013. Some exceptions were:

  • Atlantic Herring larvae were collected at relatively high densities on five occasions.
  • Sand Lance larvae were collected at relatively high densities on nine occasions.
  • Atlantic Seasnail larvae were collected at relatively high densities on two occasions in March.
  • American Plaice eggs were collected at relatively high densities twice during May.
  • Searobin eggs were collected at relatively high densities on thirteen occasions in June.
  • Atlantic Menhaden eggs were collected at an unusually high density on June 11th.
  • Winter Flounder larvae were collected at a relatively high density on June 6th
  • Hake larvae were collected at relatively high densities on eight occasions in June.
  • Cunner larvae were collected at relatively high densities on four occasions during June.
  • Atlantic Menhaden larvae were collected at relatively high densities twice in June.

Twenty-one stage one lobster larvae were collected during the Jan.-Jun. 2014 sampling period. This is the 5th highest number of lobster larvae collected during this sampling period since 2003. According to Pilgrim’s report, there has been an increase in the number of lobster larvae found in entrainment samples in recent years.


Twenty-two fish species were impinged on Pilgrim’s intake screens from Jan.-Jun. 2014, with an extrapolated total of nearly 5,000 fish. Atlantic Silversides, Grubby, Blueback Herring, Cunner and Winter Flounder accounted for 85% of this total. The extrapolated total was below average, ranking 19th out of 35 years. The mean 6-month total for 1980-2013 is 7,670 fish.

Long-term data indicate that Atlantic Silversides, Winter Flounder, Grubby, Rainbow Smelt, and Atlantic Herring have been the most numerous impinged species since 1980. From Jan.-Jun. 2014, all of these species were present. However, these 5 species were collected in numbers below their 1980-2013 semiannual means. The one except was the Grubby (473 fish) which was collected in numbers above its semiannual mean (330 fish).

From Jan.-Jun. 2014, 285 invertebrates representing 10 taxa were collected from Pilgrim’s intake screens. This resulted in an extrapolated total of nearly 8,000 animals — more than 2.5x the 1980-2013 mean of 2,710. Consistent with data from 1980-2013, sevenspine bay shrimp, squid, and cancer and green crabs were the most commonly impinged invertebrate species. Sevenspine bay shrimp accounted for 71% of the 6-month total.

Winter Flounder Tows

The waters around Pilgrim act as spawning, nursery and feeding grounds for Winter Flounder, and the species is affected by plant operations. Since the species is valuable (commercially and recreationally), it has been studied near Pilgrim since 1995. From 1995-1999, the Mass. Division of Marine Fisheries estimated the size of the Winter Flounder population near Pilgrim. Since 2000, Normandeau Associates has continued this study. In Pilgrim’s most recent Marine Monitoring Report, the winter flounder absolute abundance estimate was 65% of the 1995-2013 average of 554,778. The estimate was 74% of the long-term mean of 245,369 fish.