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West Branch Delaware River Trout Population Sampling (2010)

Mark and recapture trout population studies on the West Branch Delaware River (West Branch) have been conducted at the same four sites for most years since 1993. This effort is part of DEC's commitment to the interstate Delaware River Basin Commission (DRBC) to evaluate the effectiveness of the changing water releases program on trout populations in the 16.9 mile West Branch tailwater (water below a dam or waterpower development). In 2010, the summer base release was 325 cubic feet per second (cfs) with directed releases exceeding 1,000 cfs occurring as required (there are about 7.5 gallons per cubic foot of water). For the remainder of the year, base releases normally range from 80 cfs to 240 cfs. Summer water temperatures at the most downstream site rarely exceeds 70ºF. This tailwater river is managed as a wild trout fishery with a 12 inch size limit and 2 fish creel limit and also has a 2.0 mile Catch and Release section in Deposit.

A small boat shocker was used to collect fish at the four study sites that ranged in length from 1,884 to 4,235 feet and covered 8.7 to 19.2 acres. A total of 1,413 unmarked yearling and older trout and 107 marked trout between 4.2 and 23.2 in were collected, including 1,271 wild brown trout, 13 hatchery brown trout, 128 rainbow trout, and 1 brook trout. Thirty-three percent of all trout collected were legal size, 20% were 15 inches and larger, and 2% were 20 inches and larger.

Trout abundance at these study sites located at river mile (RM) 4.2, 8.8, 13.0, and 15.2 were 30, 79, 77, and 193 trout per acre with the trout biomass calculated to be 25.4, 50.3, 65.3, and 88.6 lbs per acre, respectively. River Miles are measured from the mouth of the river upstream. The 14 or 15 year average for the RM 4.2, 8.8, 13.0, and 15.2 study sites were 28, 63, 50, and 113 trout per acre with trout biomass averaging 25.6, 33.9, 45.9, 72.7 lbs per acre, respectively. Compared to the long term averages, trout abundance and biomass in 2010 was higher at the three upstream sites and down slightly at the downstream site. Contrary to popular opinion, trout abundance and biomass is not highest in the Catch and Release study site (RM 13.0) compared to the study site immediately upstream (RM 15.2) and has not been in all the years sampled since 1998.

Trout populations over the years have been highly variable with no apparent trends. The problem is that the releases programs implemented since 1997 have only lasted three or four years before being revised. As a result, only the younger two or three year classes are being impacted by any given releases program with the older fish the result of the prior releases programs. Biological and physical factors during these short term studies may override the benefits of the improving releases program. For example, the West Branch releases program from 2004 through 2007 recorded three of the four highest flood flows since the Cannonsville Dam was completed in 1963. The DRBC has been advised that the effectiveness of any releases program would take at least 10 years to make a determination on the benefits to the wild trout population because it would only be the last six years when all the trout through Age 5 would be the result of the releases program being evaluated. Until such a long term releases program is implemented, the DEC should end its current commitment to evaluate the impact of short term releases program to the trout populations in the West Branch.


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