Sentence:  The weekly returns will show a great falling off in the herring fishing which it may be said was a complete failure—and consequently caused a falling off of the revenues of the Harbour. There were only 521 <WSD>mease</WSD> of herrings sold at an average price of £1 2s 7¾d., or total £590. 
Meaning of the word marked with <WSD> tags:  A measure of varying quantity, often five or six (long or short) hundred, used especially when counting herring.