ML070160208

JAFNPP - SEIS Web Reference - Schaner 2004, Pelagic Planktivores, 2004, NYSDEC Lake Ontario Annual Report 2004

ML070160208
Person / Time
Site:	FitzPatrick
Issue date:	12/31/2004
From:	Prindle S, Schaner T Govt of Canada, Ontario Ministry of Natural Resources, State of NY, Dept of Environmental Conservation
To:	Office of Nuclear Reactor Regulation
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References
Download: ML070160208 (5)

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NYSDEC Lake Ontario Annual Report 2004 Pelagic Planktivores, 2004 T. Schaner ONTARIO MINISTRY OF NATURAL RESOURCES and S. E. Prindle NEW YORK STATE DEPARTMENT OF ENVIRONMENTAL CONSERVATION Introduction Sound management decisions regarding Alewife (Alosa pseudoharengus) and predator-prey balance require continued rainbow smelt (Osmerus mordax) are the monitoring of prey fish populations, and most abundant pelagic planktivores in Lake therefore starting in 1991 hydroacoustic Ontario, and the most important prey for surveys to estimate lake-wide abundance of salmon and trout. Alewife are also an pelagic prey fish have been undertaken important prey for warm water predators, jointly by the Ontario Ministry if Natural notably, walleye, and for cormorants. The Resources (OMNR) and the New York State abundance of alewife and smelt has declined Department of Environmental Conservation over the past decade, likely due to reduced (NYSDEC). Information from the nutrient loading, proliferation of non-native hydroacoustic surveys complements dreissenid mussels, and the buildup of information obtained in bottom trawling stocked salmon and trout predators. surveys conducted jointly by NYSDEC and Coincident with this decline, threespine the U.S. Geological Survey (USGS) in the sticklebacks (Gasterosteus aculeatus) have U.S. waters of the lake.

become more prominent, and in 1995-1997 there was also a temporary increase in The 2004 survey abundance of emerald shiners (Notropis atherinoides). These recent observations The 2004 hydroacoustic survey was may signal a change in the pelagic fish conducted during the period of July 20-29, community. and consisted of six cross- lake transects and an Eastern Basin transect (Fig. 1). This is The Ontario (OMNR) and New York design provides even geographic coverage, (NYSDEC) management agencies addressed and easy access to ports. It has been concerns about declining numbers of prey followed since the start of the survey series fish in 1993. At that time the number of in 1991 with only minor yearly salmonines stocked was reduced to a level modifications due to logistics. Transects that would cut the prey demand by followed a north-south line across the lake.

approximately half. Since then, however, Each night, sampling began approximately following public consultation on both sides one hour after sunset at the 10 m depth of the border, stocking levels were contour on one side, and continued across moderately increased in 1997. Furthermore, the lake to the 10 m depth contour on the since 1997 increased rates of natural other side. Sampling was usually completed reproduction of Chinook salmon have been one hour before sunrise. Acoustic data were observed. Thus the alewife and smelt collected along each transects using a populations continue to be under intense Biosonics DTX 120 kHz split beam predatory pressure. echosounder.

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NYSDEC Lake Ontario Annual Report 2004 appeared to return to the average level The analysis and interpretation of the observed over the past decade (Fig. 3).

acoustic data has been delayed this year, due to our recent discovery of possible Smelt inconsistencies between the echosounder used since 2003, and the one utilized The catches of rainbow smelt in the previously. Results from a side-by-side midwater trawls in 2004 were extremely comparison of the two systems suggest that low, similar to 2003. Most of the fish estimates from the current echosounder tend caught were 1- year olds (Fig. 4). The mid-to be lower than those from the old system. summer condition of the smelt, expressed as We are undergoing a more comprehensive the expected weight of a 120mm fish, could evaluation of potential inconsistencies not be assessed with any confidence this before finalizing the 2004 prey population year due to low sample number.

estimates. Similarly, the 2003 estimates (Schaner and LaPan 2004) will likely have Threespine stickleback to be revised in view of the new information. Threespine sticklebacks are not currently assessed from the acoustic data. They are Thirteen midwater tows using a 57m2 trawl caught in the midwater trawls, albeit not net were also conducted during the survey, efficiently, since they are too small for the to obtain samples to assess biological trawls mesh size. Nevertheless, over the attributes of the prey fish. The following years the trawls have provided a rough index brief observations are based solely on of the stickleback abundance. In 2004 trawling results. sticklebacks were caught in most tows, and the average catches were high (Fig. 5). Both Alewife the frequency of capture, and the numbers caught suggest that their abundance in 2004 The size composition of alewife caught in was higher than the average observed since the trawls (Fig. 2) suggests that older fish the sticklebacks became prominent in Lake dominated the 2004 population. Few fish in Ontario in the early 1990s.

the 120mm range, corresponding to 2- year old fish, were caught anywhere, and References although some fish under 110mm (1- year olds) were caught, they appeared to be Schaner, T., and S. R. LaPan. 2004. Pelagic limited to the Kingston Basin. planktivores. In: 2003 Annual Report, Bureau of Fisheries, Lake Ontario Unit and The mid-summer condition of adult alewife, St. Lawrence River Unit to the Great Lakes which was exceptionally low in 2003, Fishery Commissions Lake Ontario Committee.

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NYSDEC Lake Ontario Annual Report 2004 Lake Ontario Figure 1. Transects surveyed in the 2004 hydroacoustic survey.

2 1.8 Mean CUE (catch per 100m) 1.6 1.4 1.2 1

0.8 0.6 0.4 0.2 0

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 Fork Length (mm)

Figure 2. Length (FL) frequency distribution of alewife in the midwater trawl catches conducted during the 2004 hydroacoustic survey.

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NYSDEC Lake Ontario Annual Report 2004 23 22 Predicted weight of 120 mm fish 21 20 19 18 17 16 15 14 1994 1996 1998 2000 2002 2004 Figure 3. Predicted weights of 120mm (FL) alewife calculated from length-weight regressions of fish larger than 100mm captured with mid-water trawls in summer 2004 surveys. 95% confidence intervals on predicted weights are also indicated.

0.18 0.16 Mean CUE (catch per 100m) 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 Fork Length (mm)

Figure. 4. Length (FL) frequency distribution of rainbow smelt in the midwater trawl catches conducted during the 2004 hydroacoustic survey.

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NYSDEC Lake Ontario Annual Report 2004 35 100%

% of tows with 3-spine sticklebacks

% 90%

30 80%

Trawl CUE (No./100 m) 25 70%

60%

20 50%

15 40%

10 CUE 30%

20%

5 10%

0 0%

1991 1993 1995 1997 1999 2001 2003 Figure 5. Catches of threespine sticklebacks in midwater trawls conducted during the summer 2004 hydroacoustic surveys. Bars represent yearly catch per unit effort; line shows proportion of tows that contained sticklebacks. No trawls were done in 2002.

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