This was the question that I posed to Keith to prompt this segment of the DCD:
I know that you've said before that the month of May can't reliably predict the outcome of a season because we've had both high and low years start very similarly but does a large number of nests early mean more individual mommas and could mean more nests in a season in your opinion?
His reply:
To try and address your question.........
I looked at the number of nests on HI in a year versus # of unique females that hit the HI beach. You have to look at unique females using the DNA analysis and we only have basically full year data from 2010 to 2022. For about half of those years, the researchers were not able to identify the DNA in every nest - the lowest was about 97% in one year. The researchers report a ratio of Identified nests (nests with DNA analysis) to the number of "unigue" females (a female may lay up to 6 nests in a year, but not on her favorite beach). The chart shows this.
Basically, for Hunting Island that ratio is around 2 nests/unique female in a particular year. For the whole state of SC it is around 3.8 (close to 4) - capturing more of the females hitting multiple beaches. Why is HI not at 4 or 5 or 6? Because that female may lay nests on other islands nearby or in another state. Some females may only lay one nest on Hunting, while another may do 4 nests.
The largest number of nests per unique females on HI occurred in 2022 - 2.34. The lowest in 2018 at 1.46. Remember the clearly ID'd low years were 2011, 2014 and 2018. While 2011 was a low nest/female ratio year, 2014 was not particularly low.
The trend from 2018 to 2022 is upwards. So for the past couple of years, the females are laying more nests on Hunting than it would appear elsewhere - or they have a better food supply these last couple of years and can spend more energy and lay more nests period.
I can't say that a low ratio (nests/females) means a low year because 2014 was not a low ratio year but yet it was the lowest in nests during that 13-year period. The lowest ratio was in 2018, with 41 unique females, while in 2014 there were 20. The number of unique females every year jumps around. In 2022, there were 73, while in 2019 there were 77. 2016 had 70 unique females, but 2022 remains the biggest year for number of nests.
So a lot going on here. Complicated. In reality, the DNA identification of unique females doesn't help us much with predictions as we get the data too late and even if we got it earlier, whatever is going to happen is happening.
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