|Shell height frequencies for sea scallops collected in beam trawls towed in the New York & New Jersey seascapes in 2008 & 2009. At least 2 height/age classes of scallops were represented in our collections and scallops were consistently more abundant off New York.|
Fancy statistics are useful but if a data summary and simple graphs don't reveal a few intriguing trends, no amount of statistical hokus pocus will make the data interesting. So in an effort not to lose the forest for the trees below is a general summary table that I admit is a little difficult to read (The fancy statistics will come later). The table lists the percent occurrence and mean abundance of species we collected in 2 meter beam trawls in the two seascapes during 2008 and 2009 using the methods described earlier.
Species richness and patterns of age & size
Over the two years we collected 34 fish species and 19 invertebrates. Based on the animals lengths, 5 fish and 3 invertebrates were represented by more than one age class including an early juveniles less than a year old. Animals less than 1 year old are labeled age 0 in the table. For example age 0 spotted hake were represented in our trawl collections by fish less than 70 millimeters (mm) long. We collected at least two age classes of sea scallops; the youngest less than 40 mm in shell height. In addition northern sea robin, four spot flounder, black sea bass, windowpane flounder as well as rock crabs and long fin inshore squid used habitats in at least one of the seascapes as early juvenile nurseries.
The dominant fish species we collected were little skate, age 1+ spotted hake, butterfish, smallmouth flounder and gulf stream flounder. These last two species were among the 7 flatfishes occurring in our trawl samples. The butterfish we collected were all young juveniles. The most common invertebrates were seven-spine bay shrimp, sea stars, age 0 rock crabs, sand dollars, and spider crabs.
General differences between Seascapes
A number of fish species appeared to be more common in the New Jersey seascape. These included little skate, age 1+ spotted hake, bay anchovy were more common in New Jersey than New York while age-0 spotted hake collected exclusively in New Jersey over the two years. This suggests that larval delivery mechanisms and/or survival rates of newly settled spotted hake might make the New Jersey habitats more suitable nurseries. Butterfish and sand lance were also more abundant in New Jersey. Sand lance were rare in beam trawls, but these skinny little fish that live in sandy burrows were commonly captured on our underwater video and were dominant prey of the skates we collected in New Jersey during the early summer survey of 2008. The predators are always better samplers than we are. Gulfstream flounder, Red hake, age-0 searobin and striped searobin were more abundant in 2009. During that year the gulfstream flounder and red hake were more common in New York.
Among invertebrates sevenspine bay shrimp and spider crabs were more common in the New York seascape. Age-0 rock crabs, which were very important prey for many of the animals we collected, were also slightly more common in New York. Sand dollars were more abundant in New Jersey in 2008 while age-0 longfin inshore squid were more abundant in that seascape in 2009.
Sea stars were consistently more abundant in our New Jersey collections. These animals are important predators of young sea scallops. In the plot above of scallop shell heights, the smallest year class in 2008 is visible as a strong second size mode in 2009. All year classes of sea scallops were more abundant in New York than New Jersey. This might indicate that the settlement and survival of this 2008 cohort was high in New York. Differences in encounter rates of sea star predators with sea scallop prey in the two seascapes may be partially responsible for the differences in scallop abundance we observe. This is just the kind of hypothesis we can test in field experiments to identify the seascape characteristics that effect the dispersal, growth and survival of animals that use the areas as nurseries. (Thanks to Jessica Lajoie for helping to get this information together)