Need a statistician!

I've been looking at spider records from Leicestershire and Rutland (data copyright Leicestershire and Rutland Environmental Records Centre). From 1934-2009 there are a total of 40,340 records, from 2010-2019 there are 3,138 records. The phenology of records is as follows:



Plot of the new records against the old records:



From linear regression (R version 3.6.2 2019-12-12):

Multiple R-squared: 0.7861, Adjusted R-squared: 0.7647
F-statistic: 36.75 on 1 and 10 DF, p-value: 0.0001216

The p-value tests the null hypothesis that there no correlation between the variables. Rejecting this hypothesis (p <0.001), the conclusion based on this data is that the observed phenology has not changed significantly in the last decade. Note that even with my level of statistical inexpertise I have studiously avoiding imputing any cause for change, only examining whether there has been a statistically significant change in the last decade. However, Helen Smith helpfully pointed out to me that if you plot the data as percentage vales, there appears to be a "spring shift" in the last decade, even if this is not statistically significant based on available data:



NB: I have revised this post a number of times to avoid propagation of my earlier errors - many thanks to all those who have made helpful comments.