Fish Studies at the Larsen Sanctuary

Since 2010 students from Housatonic Community College, along with their professor, Dr. Tony Pappantoniou, have been engaged in studying the fish species of the Larsen Sanctuary, at Connecticut Audubon Society’s Center at Fairfield. Dr. Pappantoniou recently sent us an account of their work:

To date we have identified six species: bluegill sunfish, pumpkinseed sunfish, largemouth bass, redfin pickerel, bullhead catfish and the American eel. This grouping of fish is classified as a warm water fauna by fish biologists. Some of these species are native to Connecticut while others are introduced.

During our studies, fish are collected using seine nets, identified, photographed and measured. They are not harmed and are always returned to the location they were collected from. Here’s a rundown of what we caught.

The Centrarchid Fish – Basses and Sunfish

Bluegill Sunfish (Lepomis macrochirus):  This species was originally native to western and central North American, but it has been transplanted throughout most of the US, with Connecticut being no exception. The bluegill is commonly found in the streams and the Farm Pond of the Larsen Sanctuary. It has a fairly broad diet, consuming plant material, insects, small crustaceans and snails.

Spawning usually takes place during late June and early July. The bluegill builds a circular nest by clearing out an area of the bottom. The nests are up to 12 inches in diameter and can be easily seen if you are walking along any of the streams of the Larsen Sanctuary during breeding season. It is not unusual to see a male guarding the nest trying to attract females. Several females will deposit eggs in the same nest during a breeding season. The male guards the eggs and young for several days.  The growth of these sunfish is fairly rapid. Our own observations show that by the end of July we are collecting young that are already 1-plus inches in length (25-30 mm). The largest adult bluegill we observed was a 180 mm individual (seven inches).

Pumpkinseed Sunfish (Lepomis gibbosus): This brightly-colored relative of the bluegill is native to Connecticut. The pumpkinseed is found in the Farm Pond and the surrounding streams. The bluegill and the pumpkinseed share a lot of characteristics but can be easily told apart. The bluegill has a prominent black spot on the posterior edge of its dorsal fin along with a solid dark colored opercular flap. The pumpkinseed has a dark opercular flap with a bright red margin. The pumpkinseed also builds a circular nest similar to the bluegill and has similar breeding behavior. It is difficult to tell a bluegill nest from the pumpkinseed nest without first identifying the individuals guarding the nest.

Just as with bluegill, the young pumpkinseeds grow rapidly. We collect young in the 22–30 mm range (about 1 inch) by the end of July. The largest pumpkinseed sunfish we observed at Larsen was a 140 mm individual (5.5 inches). When we collect in early June, it is not unusual to find pumpkinseed in the 60-65 mm range. These individuals are most likely the young of the previous summer.

Largemouth Bass (Micropterus salmoides): The largemouth bass is not native to Connecticut. Biologists place this species in the same family as the sunfish. We regularly collect young largemouth bass in the streams that empty the Farm Pond. We have collected a few adults from the Farm Pond. No adults have been collected from the streams. Most likely the young largemouth bass wash into the stream during heavy spring and summer rainfalls. The small streams that extend out from the Farm Pond are not ideal habitat for the largemouth bass, as they are too shallow. Most likely the young find their way into larger streams.

We collect numerous juvenile largemouth bass over the course of a summer season and it is interesting to watch their growth progress. The following largemouth bass data is from our 2010 collecting season (1 inch = 25.4 mm):

Collection Date                                    Average Length (mm)

June 22                                                       25

June 29                                                       44

July 13                                                         50

July 27                                                         57

August 3                                                      63

This growth progression seems to be in line with other statistics reported for the largemouth bass. In a six-week span the young have more than doubled their size.

Non-Centrarchid Fish:

Redfin Pickerel (Esox americanus americanus): This species is native to Connecticut. All of the individuals collected in the Larsen Sanctuary are collected from the streams. Typical for their species, these individuals prefer small quiet sections of the streams. The redfin pickerel is an outstanding example of what biologists call a lie-in-wait predator. They remain stationary in one spot waiting for prey to come to them. When a prey is close enough they dart out and grab it with their small sharp teeth. The longest individual to date is a 133 mm specimen (5.2 inches). This species can achieve lengths of 10–13 inches.

Brown Bullhead Catfish (Ameiurus nebulosus):  The brown bullhead is a Connecticut native. Adults are collected in the Farm Pond. The largest individual we collected by seine net was 252 mm (almost 10 inches). During the summer many young catfish are collected at the outlet of the Farm Pond. Presumably they are washed out of the Pond by spring and summer rain.

Young bullheads tend to stick together during the early stages of their lives, so when we do collect them we tend to find large numbers in our seines. It is interesting to watch the progress of their growth over a summer season. The follow data is for summer 2012 (1 inch = 25.4 mm):

Collection Date            Average Length (mm)

June 17                                     17

July 8                                        23.5

July 22                                      33.4

August 5                                   38.3

August 12                                 43.5

American Eel (Anguilla rostrata):  Perhaps the most interesting of the fish living in the streams of the Larsen Sanctuary are the American eels.

All American eels undergo long distance migrations. American eels are catadromous (they swim downstream to spawn). Adult American eels from all over the east coast swim downstream and eventually end up in the South Atlantic (Sargasso Sea) to spawn. Upon spawning the adults die and the young travel back to the east coast and swim upstream to live and mature in streams and rivers.  They live in freshwater for several years until they are old enough to breed. The adults then swim downstream and back out to the Sargasso Sea to complete their life cycle. This is a truly remarkable journey for a local denizen of the Larsen Sanctuary.

American eels can grow quite large. It is not unusual for individuals to achieve lengths of two feet. The largest specimen we have collected in Larsen has been 300 mm or just under 12 inches.

American eel populations are in trouble, mostly due to damming of rivers and streams and habitat degradation in the northeast. Several years ago there was an attempt to list the American eel under the Endangered Species Act, but at the time the federal government did not see the need to do so.

The hands-on and data collecting experience my students get while working at Larsen is invaluable. Several of my students have gone on to university level programs, majoring in biology. After a day in the field one student commented: “Do people really get paid for doing this?” Could this be a future field biologist in the making?

I would like to thank Connecticut Audubon and the staff at the Fairfield Center, especially Mr. Robert Martinez, for allowing us to use this wonderful facility.

Dr. Tony Pappantoniou
Associate Professor of Biology
Housatonic Community College
Bridgeport, Connecticut
Email: apappantoniou@hcc.commnet.edu

Photos of American eel and juvenile largemouth bass are courtesy of Dr. Tony Pappantoniou. The photo of the students in the pond are by Dr. Twan Leenders/Copyright Connecticut Audubon Society