Temperature Obsessed

Disclaimer/Nerd-Alert: I am currently obsessed with water temperatures. I can’t imagine that anyone else will be even remotely as interested in this as I am. You’ve been warned. Read on if you dare…

In the classic book Carp on the Fly there is a temperature chart that lists some remarks about carp biology corresponding to different water temperatures. The data has no attribution, but I have confirmed most of the information with additional sources, especially a series of YouTube interviews with Dr. Simon Scott, a biologist and carp aquaculturist in the UK. I have also compiled some data mined from John Montana’s old blog regarding his observations of carp in the Columbia River. Below is a chart that lists the first time each year that he mentioned seeing carp exhibiting spawning behavior on the river. Alongside that I have included corresponding Army Corps of Engineers water temperature data, and recorded air temperatures from the Portland Airport.

Date spawning behavior observed (source: carponthefly.blogspot.com)	USACE Water Temp Data ℉	PDX air temp hi/low ℉
April 29, 2007	51 – 52.4	65/49
May 16, 2008	53.2 – 55.6	92/57
April 5, 2009 (“pre-spawn”)	42.9 – 45.1	71/41
May 14, 2010	52.6 – 55	76/50
May 10, 2011	50.3 – 51.9	64/48
April 28, 2012	50.8 – 51.6	64/48
April 22, 2012	48.8 – 49.7	82/50
April 27, 2013	50 – 51.6	72/45
April 20, 2014	47.7 – 50.4	64/44

The glaring thing about this data is that is disagrees completely with what we know about carp spawning behavior, namely that they require water temperatures of at least 60 degrees to trigger spawning! The most likely explanation is that the temperature of the shallow water where the carp spawn is not the same as the well mixed water just below The Dalles Dam, where these USACE measurements were taken. To test this theory, I have been taking surface water measurements in the river this winter.

This pretty clearly shows that there is a difference between the USACE data and the temperature near the surface of the river away from the dam(s). Not surprisingly, the spawning observations imply that during the spring, when the weather is warming, the surface temperatures are greater than the mixed water temperatures, while my wintertime data implies that during cooling weather, the surface temperatures are lower than the mixed water temperatures.

What this all means right now is that the carp in the Columbia River are probably still holding in deep water where the temperatures are slightly warmer than in the shallows. The chart from Carp on the Fly claims that the fish will begin a “pre-spawn move to the shallows” when the water temperatures reach 41 degrees. We are very nearly there. However, I don’t think the carp will really show up until the shallows are definitely warmer than their deep winter holding areas, which may happen at a slightly higher temperature.

Another excavation of John Montana’s blog reveals that the fishing season should pick up once the USACE data is consistently over 43 degrees (more specifically 46.3 ± 3 degrees). I don’t know what actual surface water temperatures will correspond to this threshold, but I do know that historical USACE data indicates it will likely happen in March, and can happen fairly quickly, over the course of a week or even a few days. For the past few weeks I have been checking many spots for signs of fish. So far, I haven’t seen a single carp in the river, but today the USACE recorded water temperatures over 42 degrees for the first time this year, so it may happen soon.

Okay, for those who actually scrolled through all that, here are some pretty pictures: