ML070160209

JAFNPP - SEIS Web Reference - Schaner 2005, Pelagic Planktivores, NYSDEC Lake Ontario Annual Report 2005

ML070160209
Person / Time
Site:	FitzPatrick
Issue date:	12/31/2005
From:	Lapan 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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Download: ML070160209 (5)

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NYSDEC Lake Ontario Annual Report 2005 Pelagic Planktivores T. Schaner Ontario Ministry of Natural Resources Picton, Ontario K0K 2T0 S. R. LaPan New York State Department of Environmental Conservation Cape Vincent, New York 13618 Alewife (Alosa pseudoharengus) and rainbow hydroacoustic surveys complements information smelt (Osmerus mordax) are the most abundant obtained in bottom trawling surveys conducted pelagic planktivores in Lake Ontario, and the jointly by NYSDEC and the U.S. Geological most important prey for salmon and trout. Survey (USGS) in the U.S. waters of the lake.

Alewives are also important prey for warm water predators, notably, walleye, and for Methods cormorants. The abundance of alewife and smelt has declined over the past decade, likely New survey design due to reduced nutrient loading, proliferation of Before 2005 the surveys followed established non-native dreissenid mussels, and the buildup transects with only minor yearly modifications of stocked salmon and trout. As alewife and due mostly to logistics. This was a practical smelt declined, threespine sticklebacks approach dictated by harbor locations, running (Gasterosteus aculeatus) have become more times, and the limited period of darkness in the prominent. These recent observations signal a summer. A statistically preferable random-change in the pelagic fish community. transect design was deemed impractical. In 2005 we modified the fixed transect design to include Concerns for declining numbers of prey fish a random element. Five fixed cross-lake were addressed by the Canadian and U.S. corridors approximately 15 km (9.6 mi) wide management agencies in 1993, when the number were established (Figure1) based on logistic of salmonines stocked was reduced to a level constraints, but within these corridors transects that would cut the prey demand by are selected at random. A single east-west offset approximately half. In 1997, however, stocking is randomly chosen, determining the relative levels were moderately increased following position of all transects within their respective public consultation on both sides of the border. corridors, and thus the survey is essentially a Furthermore, since 1997 increased rates of systematic survey with a random start.

natural reproduction of chinook salmon have been observed. Thus the alewife and smelt New midwater trawl populations continue to be under intense A remotely opening/closing Tucker trawl was predatory pressure. tested during the 2005 survey in place of the 57 m2 (613.5 ft2) midwater trawl used in previous Sound management decisions regarding surveys. The net has a 2 m2 (21.5 ft2) square predator-prey balance require continued opening and is constructed of 1.6 mm (0.06 in) monitoring of prey fish populations; therefore, knotless mesh forming three 8.5 m (27.9 ft) long starting in 1991 hydroacoustic surveys to cod ends. The theoretical advantages of this gear estimate lake-wide abundance of pelagic prey are its ability to catch small fish that are not fish have been undertaken jointly by the Ontario efficiently captured by the midwater trawl and Ministry if Natural Resources (OMNR) and the the ability to sample discrete depth layers New York State Department of Environmental without catch contamination during deployment Conservation (NYSDEC). Information from the and retrieval. Although the relatively small Section 3 Page 1

NYSDEC Lake Ontario Annual Report 2005 opening and fine mesh size of the Tucker trawl Results and Discussion make it less suitable for capture of adult alewife and smelt, a need exists to investigate species Consistency across the hydroacoustic survey composition and vertical distribution of smaller time series acoustic targets detected in great abundance. In 2003 the Simrad EY500 120 kHz split beam echosounder was upgraded to Biosonics DTX The 2005 survey 120 kHz split beam, and new analytical software The 2005 hydroacoustic survey was conducted was utilized. Informal comparisons between the during the period 25 July to 2 August, and two systems in 2004 suggested that the new consisted of five cross-lake transects and an sonar/software combination yielded lower Eastern Basin transect (Figure 1). Each night, estimates than the previous system; therefore, sampling began approximately one hour after results of the 2004 survey were not published.

sunset at the 10 m (39.4 ft) depth contour along Extensive comparisons between the two systems the New York or Ontario shore, and continued in 2005 confirmed earlier observations, and across the lake to the 10 m depth contour on the revealed complicated relationships between the opposite side. Sampling was usually completed two systems, dependent upon particulars of the one hour before sunrise. Acoustic data were signal processing stage, as well as the collected along the transects using a Biosonics composition and depth distribution of the target DTX 120 kHz split beam echosounder. populations. Due to the aforementioned, Temperature profiles were measured at several correction factors cannot be readily established points along each transect. between the two systems. It appears, however, that the differences are at most 30% (i.e. the new Raw acoustic data were stratified based on system yielding 30% lower density estimates) thermal layer, bottom depth and geographical but are generally less. The potential bias of this zone. Data were processed with Echoview magnitude does not substantially alter software by Sonardata, using -64dB volume interpretation of the population trends; therefore, backscattering strength and target strength the results from the two time periods are thresholds. The resulting scaled integrated reported without corrections.

voltage estimates of total target abundance were split into 3dB target strength (TS) bins according Alewife to results of single-target analysis. Abundances The 2005 midsummer abundance estimate of of yearling and older fish (YAO) were extracted YAO alewife was 72 million fish (Figure 2).

from the resulting target strength histograms. In Using the average weight of YAO alewife from the upper layer (epilimnion plus metalimnion) 1997-2002 (no data available for 2005), this the histograms were processed to identify translates into a biomass estimate of 1,797 component modes, and targets in the mode at or metric tons (3.96 million pounds). Isolation of below -38dB were assumed to be yearling and acoustic targets corresponding to YAO alewife older (YAO) alewife. In the lower layer was especially problematic in 2005 (due to (hypolimnion) all targets larger than -55dB were target size overlap and unusually low numbers assumed to be YAO smelt. of YAO targets); therefore, an alternate 2005 estimate was made using target separation Eight midwater tows, each sampling three criteria from previous years, yielding an estimate discrete depths, were made with the Tucker of 124 million fish or 3,088 metric tons (6.81 trawl during the survey. An additional three million pounds) (Figure 2).

tows were made with the 57 m2 midwater trawl at the end of the survey. Either estimate suggests a very low, possibly the lowest, population since the start of the series in 1997 and the third consecutive year of extremely low levels. Corresponding estimates from spring bottom trawls (OGorman et al. 2006) also indicate generally low population levels in the Section 3 Page 2

NYSDEC Lake Ontario Annual Report 2005 recent years, but not as extreme as seen in the estimated from acoustics and volumes filtered midsummer acoustic series. A high degree of by the trawl indicated that these catches were in concordance exists between the two series for line with the density of available fish.

the years 1997-2002 (unpublished data), but the acoustic series shows a relatively greater decline It is particularly noteworthy that YOY alewives, in the recent years. Anecdotal data from other smelt, as well as threespine sticklebacks of all sources, such as the recent poor condition of sizes were found in all three thermal layers, Chinook salmon (Ministry of Natural Resources. although the hypolimnion appeared to be the 2005), and recent high condition of alewife in least preferred by all three species. YOY smelt fall (OGorman et al. 2006) is consistent with were found evenly throughout the epi- and the possibility of record low alewife levels; metalimnion, while threespine sticklebacks were therefore, the predator-prey balance in the lake found mostly in the metalimnion. Catches of should continue to be closely monitored. YOY alewife were lower, and quite similar between the three layers. The majority of fish Rainbow smelt caught in the Tucker trawl were less than 60 mm The 2005 midsummer abundance estimate of (2.4 in) long, but a few adult smelt were caught YAO smelt was 304 million fish (Figure 3). indicating that the gear may be suitable for Using the average weight of YAO smelt from monitoring all sizes of smelt. No adult alewives 1997-2001 (no midsummer data available for were caught, suggesting net avoidance or low 2002-2005), this translates into a biomass density. Despite the low catches, the Tucker estimate of 2,028 metric tons (4.47 million trawl promises to be valuable tool in interpreting pounds). The population has increased in 2005 the distribution of small targets detected by from two previous low years to a level similar to acoustics.

the early 2000s.

References Midsummer acoustic smelt estimate trend also agree well with that seen in the spring bottom Ministry of Natural Resources. 2005. Section trawls, with the exception of the low acoustic 2.9 in Lake Ontario Fish Communities and 2004 estimate (Walsh et al. 2006) (Figure 3). Fisheries: 2005 Annual Report of the Lake That year, yearlings accounted for a high Ontario Management Unit. Ontario Ministry of proportion of the YAO population (OGorman et Natural Resources, Picton Ontario, Canada.

al. 2005), and the method used to isolate YAO targets apparently failed to fully include OGorman, R., R.W. Owens, S.E. Prindle, J.V.

yearlings either due to their small size or their Adams, T. Schaner. 2005. Status of major prey higher position in the water column. The fish stocks in the U.S. waters of Lake Ontario, increased abundance seen in the 2005 acoustic 2004. Section 12 in 2004 NYSDEC Annual survey is likely due to these fish, now detectable Report, Bureau of Fisheries, Lake Ontario Unit as two-year olds. and St. Lawrence River Unit to the Great Lakes Fishery Commissions Lake Ontario Committee.

Threespine stickleback The abundance of threespine sticklebacks was OGorman, R., M. Walsh, T. Strang, S.E.

previously monitored in the 57 m2 midwater Prindle, J.V. Adams, T. Schaner. 2006. Status trawl catches that accompanied the acoustic of major prey fish stocks in the U.S. waters of survey. due to an insufficient number of 57 m2 Lake Ontario, 2005. Section 12 in 2005 midwater trawl tows. NYSDEC Annual Report, Bureau of Fisheries, Lake Ontario Unit and St. Lawrence River Unit Tucker trawl trials to the Great Lakes Fishery Commissions Lake Catches in the Tucker trawl were quite low, Ontario Committee.

averaging 7 fish per 15 min deployment of a cod Walsh, M.G., R. OGorman, A.P. Maloy, T.

end (up to three cod ends fished per trawl). Strang, and S.E. Prindle. 2006. Status of Calculation based on typical target densities Section 3 Page 3

NYSDEC Lake Ontario Annual Report 2005 rainbow smelt in the U.S. waters of Lake Ontario, 2005. Section 12 in 2005 NYSDEC Annual Report, Bureau of Fisheries Lake Ontario Unit and St. Lawrence River Unit to the Great Lakes Fishery Commissions Lake Ontario Committee.

Figure 1. Transects surveyed in the 2005 hydroacoustic survey. Also shown are sampling corridors established in 2005, from which the transects in the main lake are randomly chosen.

Section 3 Page 4

NYSDEC Lake Ontario Annual Report 2005 2.0 25000 20000 1.5 Abundance (billions Abundance (billion)

Biomass Biomass Biomass (MT) 15000 1.0 10000 0.5 5000 Abundance 0.0 0 1997 1998 1999 2000 2001 2002 2003 2004 2005 Figure 2. Abundance and biomass of yearling-and-older alewife. Abundance estimates were obtained directly from hydroacoustic surveys, biomass estimates were obtained by applying average weights measured in midwater trawls to abundance estimates. Average weights used in biomass calculations in 2002, 2004 and 2005 were based on pooled data from other years. Two abundance and biomass estimates are shown for 2005; the second (higher) set of estimates was based on peak-separation criteria from other years, and was produced due to uncertainties in separating alewife targets using within-year information.

2.5 8000 7000 2.0 6000 Abundance (billions Biomass (MT)

Biomass (MT)

Abundance (billion) 1.5 5000 4000 1.0 Biomass 3000 2000 0.5 Abundance 1000 0.0 0 1997 1998 1999 2000 2001 2002 2003 2004 2005 Figure 3. Abundance and biomass of yearling-and-older rainbow smelt. Abundance estimates were obtained directly from hydroacoustic surveys, biomass estimates were obtained by applying average weights measured in midwater trawls to hydroacoustic abundance estimates. Average weights used in biomass calculations in 2002 through 2005 were based on pooled data from other years.

Section 3 Page 5