PART IV. LIMNOLOGY AND ITS RELATION TO SOCKEYE SALMON 



Limnological data were collected in 1957 

 concurrently with studies of the biology of 

 sockeye salmon discussed in Parts I, 11, and 

 111. One form of Liebig's Law, or the Law of 

 the Minimum, states that productivity is lim- 

 ited by the nutrient present in the least 

 amount at any given time. If one essential 

 element is in short supply, regardless of the 

 abundance of other essential elements, pro- 

 duction may be limited. Part IV describes the 

 limnology of the lake and stream environments 

 and the significance of selected key factors, 

 including nutrients, in the biology of sockeye 

 salmon (fig. 27). 



The objectives of the studies were to: 



(1) Measure relative seasonal abundance of 

 zooplankton and phytoplankton at three repre- 

 sentative stations and relate to the distribu- 

 tion and the diet of juvenile sockeye salmon; 



(2) determine the bottom morphometry of 

 Brooks Lake by surveys with a recording echo 

 sounder; (3) determine the relative abundance 

 of bottom fauna and through food studies, 

 relate to utilization by sockeye salmon; (4) de- 

 termine the following qualities that influence 

 productivity by analyzing lake water at 2-week 

 intervals at representative midlake stations — 

 temperature, phosphorus, nitrogen, silica, tur- 

 bidity, transparency, oxygen, hydrogen ion 

 concentration, and alkalinity and total hard- 

 ness; (5) determine the primary productivity 

 of Brooks Lake by the carbon^ ^ method; 

 (6) record continuously the temperature of 

 the gravel water of Brooks River and One 

 Shot Creek; (7) record fluctuations in lake 

 level; and (8) record climatological data and 

 solar radiation. 



TURBIDITY 

 TRANSPARENCY 



FISH (tockty* •olmon) 



ZOOPLANKTON - INSECTS 



PHYTOPLANKTON (dlotont) 



TEMPERATURE 

 OXYSEN 

 pH 



ALKALINITY PHOSPHORUS NITROSEN SILICA TOTAL HARDNESS 



Figure 27,-- Probable relation of sockeye salmon pro- 

 duction and chemical and physical water qualities in 

 Brooks Lake. 



PLANKTON AND ITS RELATION TO 

 JUVENILE SOCKEYE SALMON 



Information was needed on the kinds and 

 abundance of zooplankton in Brooks Lake be- 

 cause, as previously discussed in Part III in 

 the section on food of juvenile sockeye salmon, 

 it is an important food item. Phytoplankton 

 are not usually eaten by juveniles, but infor- 

 mation on kinds and abundance gives useful 

 clues to basic productivity and to limiting 

 chemical constituents of the water. 



Beginning June 27, when weather permitted, 

 plankton collections were made at 10-day in- 

 tervals at three stations (fig. 21). Zooplankton 

 was collected with a Clarke- Bumpus sampler 

 with a number 10 net, and phytoplankton was 

 collected with a 3-liter Kemmerer water 

 sampler. 



Station I was located on the edge of the 

 littoral area in 5 m. of water; station II, 

 southwest of station I in 35 m.; and station III, 

 in midlake southwest of station II in 67 m. 

 Depths sampled were as follows: station I, 

 surface and 5 m.; station II, surface, 5, 10, 

 and 25 m.; station III, surface, 5, 10, 25, 35, 

 and 50 m. All tows were made between 10 a.m. 

 and 1 p.m. 



Zooplankton 



The Clarke- Bumpus sampler was an open, 

 nonclosing type and was operated according 

 to recommendations of the inventors (Clarke 

 and Bumpus, 1950). To ensure that the mouth 

 of the instrument remained perpendicular to 

 the flow during horizontal tows and to prevent 

 water from entering the net while it was being 

 raised or lowered to the desired sampling 

 depth, a 20-pound weight was fastened to the 

 lower edge of the sampler frame. 



After each haul the net and bucket were 

 rinsed with lake water and the contents drained 

 into a small screw-top jar containing a solu- 

 tion of 3 percent formalin. Plankters were then 

 transferred to an alcohol solution for storage 

 until counts and identifications could be made. 

 Identifications were made from keys by Pennak 

 (1953). Numbers of plankters were estimated 



43 



