| Abstract/Description or Keywords |
Early study years focused on gaining a better understanding of whole lake biological relationships, as well as identifying limiting factors and remedial measures that should result in recovery of the lakes kokanee populations. Loss of kokanee spawning habitat, lake water nutrient imbalance resulting in a decline of lake productivity and mysid competition with kokanee for preferred macrozooplanktors have jointly caused a dramatic decline of Okanagan Lakes kokanee population over the last three decades. Fundamental to recovery of kokanee has been protection and restoration of kokanee spawning habitat. OLAP investigators recognized that a combination of lake and stream restoration measures were required if a long term kokanee recovery was to be achieved. Several restoration projects have been completed as a result of the first phase of Okanagan Lake studies. The first and most obvious step has been recovery of water for fish spawning in tributaries flowing into Okanagan Lake. Progress has been made, particularly for the largest stream, Mission Creek, but further efforts are required on several other spawning streams. Aside from Mission Creek, Trout Creek has been singled out as having the greatest potential for kokanee restoration. On these streams some flow improvements have been achieved by working with the large water users. Extreme heat and drought conditions from 2003-2005 underscored the importance of working towards adequate water flow in fish spawning streams. During these years several of the smaller streams that are over used by public consumption (domestic and agricultural) were virtually dry at the time of kokanee spawning. Stream habitat restoration has also begun, again mostly in Mission and Trout Creek watersheds and recently in Penticton Creek. Kokanee escapement data over several decades indicates that in-lake survival has often been low resulting in fewer spawners than their parental numbers. Poor kokanee fry-to-adult survival indicates that the quality and or quantity of food in the lake have been responsible for continued low spawner numbers. For this reason, the second phase of OLAP that began in 2001 has focused on understanding the N:P imbalance in the lake and how it may impact primary and secondary production. Limnological monitoring over a number of years indicated that Okanagan Lake appeared to be primarily nitrogen limited during the growing season. From 2003-2005 Okanagan Lake suffered drought conditions and the limnological data indicated a considerable decrease in nutrient concentrations that resulted in extremely low algal production. Okanagan Lake is somewhat unusual as the lake becomes depleted of NO3 in the epilimnetic zone by early summer. The last nine years of data indicates that the N:P ratio is out of balance for growth of algae preferred by macrozooplanktors (especially Daphnia) that are in turn preferred by kokanee. The 2005 kokanee escapements were the highest in two decades but still far below the levels recorded in the 1970s and early 1980s. Shore spawner counts continue to be problematic but the 2005 results were encouraging with a sizeable increase recorded. These results contradict the limnological data that suggest poor growing conditions prevail in the lake. Although entirely speculative, increased numbers of kokanee during the last three years may be due to decreased mysid numbers during 2002-2004. The 2005 mysid densities were again quite high so the 2006 kokanee escapements should be quite informative. |
