Table 1.

Locations of sampled sites and sample numbers

System	Tributary	Population	Grid ref.	Code	n	HO	HE	AR	FIS
Western Cleddau	Upper Western Cleddau	Withy Hill	SM904297	WH	26	0·366	0·408	1·851	–0·291
		Priskilly Forest	SM919299	PF	21	0·130	0·122	1·461	–0·062
		Welsh Hook	SM932278	WHK	20	0·140	0·164	1·636	0·149*
	Afon Anghol	Little Newcastle	SM979289	LN	19	0·202	0·149	1·547	–0·377
		Sealyham Bridge	SM967279	SHM	24	0·175	0·118	1·358	–0·500
	Lower Western Cleddau	Treffgarne Bridge	SM959230	TB	21	0·195	0·175	1·556	–0·116
		St. Catherine's Bridge	SM945198	SCB	18	0·152	0·206	1·578	0·267*
		Haverfordwest playground	SM953161	PG	17	0·194	0·221	2·027	0·127**
		Haverfordwest car park	SM953164	CAR	15	0·223	0·234	1·993	0·045
Tempo/Colebrooke	Tempo	Drumderg	H341446	DRD	30	0·262	0·217	1·572	–0·211
		Cornafannoge	H335426	CFG	30	0·205	0·194	1·500	–0·053
		Killynure Bridge	H339388	KYB	21	0·222	0·222	1·600	–0·001
		Ballyvelin Bridge	H334372	BYB	30	0·174	0·292	2·170	0·410***
	Upper Colebrooke	Ashbrooke	H392442	ASH	30	0·266	0·282	2·115	0·057**
		Tullyreagh Bridge	H379442	TLY	30	0·273	0·303	2·149	0·100***
		Ardunshin	H372426	ARD	35	0·231	0·231	1·885	0·003
		Littlemount Bridge	H370405	LMB	31	0·245	0·257	2·121	0·045
		Maguiresbridge	H350387	MAG	30	0·282	0·328	2·327	0·145***
	Lower Colebrooke	Ballindarragh Bridge	H331360	BDB	30	0·257	0·326	2·526	0·215***

n, number of individuals sampled; H_O, expected heterozygosity; H_E, expected heterozygosity; A_R, allelic richness; F_IS, inbreeding coefficient. *P < 0·05; **P < 0·01; ***P < 0·001.